Car air conditioning system operation

Air conditioning is a system used to create and maintain a comfortable driving environment inside a vehicle. It does this by transferring the heat from inside a vehicle to the outside keeping the temperature down inside the car.The system cools, dries and cleans the air.

The most basic systems have manual temperature control but systems are becoming more and more complex with full climate control on a lot of modern cars which rely on a lot of sensors to maintain the selected temperature.

Air conditioning system schematic diagram-basic system

Common Air conditioning problems

Air conditioning system not cold enough

The Air Conditioning system in your vehicle is not usually covered by most manufacturers servicing schedules and the refrigerant gas that is used to operate the system depletes over time. On average most vehicles lose up to 15% per annum this problem can be caused when then system is not used during the winter months allowing the small “O” ring seals to dry out resulting in a gradual deterioration in system performance eventually resulting in the system being too low to operate at all.

Most problems of this type can be put right fairly easily by a leak check of your system followed by a complete refill of your air conditioning refrigerant, this is sometimes referred to as a re-gas. Please contact usfor your air con annual service or re-gas if you live in the Cardiff,Swansea, Bridgend or Newport area.

Air conditioning system smells odd

If you notice any strange smells when you put your air-con on then this could be signs of bacteria build up on your system.

As systems become older or are used infrequently the air conditioning system can start to develop bacteria, micro organisms and even mould or fungi growing especially behind the dash panel on the evaporator, this can lead to some very unpleasant odours. Some even claim this can result in headaches and flu like symptom sometimes referred to as sick car syndrome.

Don’t suffer any longer air con systems can be treated effectively with an anti-bacterial treatment that destroys the bacteria growth and leaves your car smelling fresh again.

The earlier this is treated the better you will feel!

Please call for a quote. from one of our mobile air con repair technicians.

If your air-con system suddenly starts making noises you have not heard before it is very advisable to have a qualified vehicle air conditioning specialist to have a look at it.

Some noises could be early symptoms of a compressor failure (the compressor is the air conditioning pump).The compressor is usually the most expensive part on the system ranging from approximately £230 to £600+ and if the bearings in your compressor break down or if the compressor seizes up it also means that other components can become contaminated with metal particles A flush of the system would then be needed as well as replacement of the compressor, the receiver / drier and the expansion valve - quite a hefty repair bill!
Its not all bad news however - some noises are quite normal

There are 2 different types of air-con system operation some vehicles use a system where the compressor (pump) cycles on and off which means that there is a clicking noise heard every few seconds this is normal, however if this switching cycle changes noticeably or the air con is not very efficient this could be an early symptom of low refrigerant or low gas pressure.
Pool of water underneath the car after using air-conditioning
You will sometimes see a water puddle on the ground, usually under the passenger footwell area, this is a normal feature of the air conditioning system as it is only water dripping from the air conditioning evaporator which has a drain tube fitted to allow the condensation from the evaporator to drain away from the vehicle.
Damp carpet in the footwell or excessive misting of the windscreen

Sometimes the drain tube from the evaporator may become blocked or detached allowing the condensation to build up inside your evaporator if this occurs water will just build up inside your car to a point where there are damp carpets or misting / high humidity type problems.

Electrical Charging System Basics

Charging System Basics:

The electrical system in an automobile is said to be a 12 volt system, but this is slightly misleading. The charging system in most cars will generally produce a voltage between 13.5 and 14.4 volts while the engine is running. It has to generate more voltage than the battery's rated voltage to overcome the internal resistance of the battery. This may seem strange, but the current needed to recharge the battery would not flow at all if the charging system's output voltage was the same as the battery voltage. A greater difference of potential (voltage) between the battery's voltage and the alternator's output voltage will provide a faster charging rate.

As long as the engine is running, all of the power for the accessories is delivered by the alternator. The battery is actually a load on the charging system. The only time that the battery would supply power with the engine running is when the current capacity of the alternator is exceeded or when engine is at a very low idle.

Alternator Basics

Overview:

A basic alternator has 2 main electrical components. The rotor and the stator. The rotor is the part of the alternator that is spun by the drive belt. There are a group of electrical field coils mounted on the rotor. The stator is the group of stationary coils that line the perimeter of the inside of the alternator case. When current (supplied by the voltage regulator - to be explained later) is flowing in the rotor's coils, they induce current flow in the stationary coils. The induced current (and voltage) is an AC current. To convert this to DC, the current is passed through a bridge rectifier.

Stator and Rotor in Action:

In the following diagram, you can see three crudely drawn sets of rotors and stators. In the leftmost diagram (marked 'A'), you can see the rotor's coil approaching the stator coil. As the rotor coil approaches the stator coil, it induces current flow in the stator coils. This causes an increase in output voltage. As it approaches the position where the coils' centers are aligned ('B'), there is no induced current. When the coils move away from each other ('C') the induced current flows in the opposite direction and the generated voltage is negative.

Rectification:

You should have noticed that the generated voltage was AC. You already know that a vehicle's charging system needs to produce DC to recharge the battery. This is done with diodes. The following diagram shows a simple transformer and a bridge rectifier. The transformer is driven with a sine wave (similar to that produced in each stator coil). Since the transformer is driven with a sine wave, the output of the transformer is a sine wave (similar to the one shown). The sine wave is driven into the bridge rectifier and the output is a pulsed DC waveform.

Bridge rectifier:

You should also realize that there are 3 different groups of stator coils in an alternator (not shown in diagrams). The rectification is much like the simple transformer shown above but in the place of a single transformer winding there are 3 windings. It also uses 6 diodes instead of 4.

3 Phase:

The following diagram shows the 3 different phases from the 3 groups of stator windings. The three phases of AC are shown in three different colors. The next set of lines shows the rectified waveforms overlapped. The bottom waveform (white line) is what the rectified voltage would actually look like if viewed on an oscilloscope. Connecting the battery to the alternator will smooth the white line even more.

Alternator Schematic:

The following is a generic schematic showing the stator windings and the bridge rectifier. You also see a diode trio. the diode trio takes part of the output and sends it to the voltage regulator. The output diodes are the rectifiers that rectify the AC and supply power to your electrical accessories.

Brushes and Slip Rings:

For an alternator to produce electrical current, there needs to be some excitation current flowing in the rotor windings. Since the rotor is spinning, you can't just connect a couple of wires to it (cause they'd just be twisted off :-). To make the electrical connection, slip rings and brushes are used. The slip rings are fixed to the shaft of the rotor. The brushes are fixed to the stationary part of the alternator. The brushes, which are generally made of carbon, are spring loaded to keep constant pressure on the slip rings as the brushes wear down. The following diagram shows the general location of the rotor and the associated parts.

Voltage Reguation:

As you already know from the 'wire' page, all wire has resistance. You also know that when you have current flow through a resistive element (wire), there will be a voltage loss. If the current draw from the charging system was constant, there would be no need for a voltage regulator. If there was no loss, the design engineer would simply design the alternator to produce a given voltage. This won't work with a car audio system because the current draw is anything but constant. This means that the alternator needs a compensating voltage regulator. The voltage regulator controls the flow of current in the rotor's windings. The voltage regulator's output current will typically be between 0 amps (with little or no current draw) and 5 amps (at maximum current draw). The regulator can vary the current flow infinitely to keep the voltage precisely at the target voltage. Generally the regulator is built into the alternator. There are some high current/special use alternators which may have external regulators. Some of the external regulators are adjustable via a potentiometer.

Current demand and flow:

If you have an alternator that can produce 120 amps of current (max) and the the total current demand from the electrical accessories (including the battery) is only 20 amps, the alternator will only produce the necessary current (20 amps) to maintain the target voltage (which is determined by the alternator's internal voltage regulator). Remember that the alternator monitors the electrical system's voltage. If the voltage starts to fall below the target voltage (approximately 13.8 volts depending on the alternator's design), the alternator produces more current to keep the voltage up. When the demand for current is low, the full current capacity of the alternator is not used/produced (a 120 amp alternator does not continuously produce 120 amps unless there is a sufficient current draw).

Dimming lights:

When you play your system at very high volumes and the lights on your vehicle dim slightly, it generally means that your alternator can not supply enough current for all of your electrical accessories (including your amplifiers). If you play a long bass note/tone and the lights get dim and stay dim until the note is over, your alternator clearly can not keep up with the current demand. If, on a long bass note, the lights dim just for a fraction of a second but return to their original brightness while the note/tone is still playing, the alternator's regulator may just be a little slow in reacting to the voltage drop. Since the lights return to their original brightness during the bass note, the alternator is able to supply the current needed by your power your amplifiers and other electrical accessories.

Warning!

Some people tell you that you can check your alternator by disconnecting it from the battery to see if the alternator can produce enough current to keep the engine running. BAD IDEA!Disconnecting the battery will subject the voltage regulator (and computer and audio equipment...) to significant voltage spikes which may cause an otherwise good alternator to fail. Even if there were no damaging spikes, this test would not indicate whether or not the alternator was good because the engine will easily run with a weak or failing alternator.

Simple Test:

If you want to see if your alternator is producing current, turn on your headlights when you're parked and the engine idling with the headlights shining on a wall (at night). Notice how bright they are. Then turn the engine off. The lights should get dimmer when you turn the engine off. If the lights get brighter when you kill the engine, the alternator was not charging sufficiently. When doing this test, the lights should be the only load (turn the stereo, a/c and other accessories off). With a heavy load, an otherwise good alternator may not be able to produce sufficient amounts of current at idle.

Basic Battery Information

Battery Construction:

A standard 12 volt cranking battery has 6 individual cells. Each cell is designed to produce ~2.1 volts. The cells are connected in series for a total of about 12.5 volts. Each cell basically consists of 1 set of lead plates and 1 set of lead plates coated with lead dioxide submerged in a sulfuric acid electrolytic solution.

Electrolyte Levels:

The level of the electrolyte should be about 1/8" below the bottom of the filling wells. If the electrolyte is above the bottom of the well, it may be forced out when the battery is charged. If the electrolyte is allowed to fall to below the top of the plates, the battery will be damaged. If the level of the electrolyte is low, refill it with distilled water only. Regular tap water has minerals which may coat the plates and reduce the battery's capacity.

Distilled Water:

Distilled water is water that's been heated to cause it to evaporate into water vapor. The water vapor is then condensed back into liquid water. The distilled water is free of all impurities including minerals that would coat the plates of the battery and therefore reduce its capacity to produce electrical current.

Cranking Amps:

Cranking amps is the spec that tells you how much current a battery can produce for 30 seconds at a temperature of 32° F and not have the voltage on any of the individual cells drop below 1.2 volts (7.2 volts for a 6 cell automotive battery). This may also be known as MCA or marine cranking amps.

Cold Cranking Amps:

This is the same test as cranking amps but is done at 0° F. The CCA spec is especially important if you live in a really cold climate. Since the chemical reaction that produces electrical current in the battery slows down as the temperature drops, the battery can produce less current at colder temperatures (especially below freezing). When comparing the current capacity of batteries, make sure that you have some standards to qualify the current ratings. If you see the current rating without CA or CCA, you don't know how the battery was tested and the current rating is virtually useless.

Reserve Capacity:

The reserve capacity is the time that a battery can produce 25 amps at 80° F before the individual cell voltage drops below 1.75 volts (10.5 volts for a 6 cell automotive battery).

Deep Cycle vs Standard Battery:

1. A normal lead-acid battery will be damaged if it is completely drained (even if it's only one time).
2. A deep cycle battery is designed to survive being drained multiple times.
3. Deep cycle batteries have more reserve capacity but have less cranking amps for a given size.
4. A standard battery would have more total surface area on its plates when compared to a deep cycle battery of equal size. This extra surface area provides more area for the chemical reaction to take place and therefore produce a higher output current.
5. The electrolyte in a deep cycle will be a slightly more concentrated sulfuric acid than a standard battery.

Gel-cell Batteries:

Gel-cell batteries use a thickened (gelled) electrolyte that will not leak out like a liquid electrolyte. Many of them can be mounted in virtually any position. These batteries may be suitable for some applications but for engine starting, other batteries should be used. Gel-cell batteries can not produce as much current for long periods of time as standard liquid electrolye batteries.

Recombinant Gas Batteries:

RG batteries have only 2 long thin plates per cell. They are constructed much like anelectrolytic capacitor. The plates are separated by a fiberglass mat material designed to hold the electrolyte. These long thin plates have significant amounts of surface area (compared to standard batteries). This extra surface area allows the battery to produce significantly more current than standard batteries of similar physical size. Optima^® is one manufacturer of RG batteries. If you're going to add batteries to your system and the batteries will be in the vehicle's trunk or passenger compartment, RG batteries won't vent flammable hydrogen gas or corrosive gasses into the vehicle.

Group Size:

The battery group size is an indicator of the battery's physical dimensions.

Understanding Alternators - an Overview

ALTERNATOR WARNING LIGHT

"What does that little red light that says ALT mean when it comes on?" Very basically, it means that either the alternator output voltage is lower than the battery voltage, or the battery voltage is lower than the alternator output voltage. If the light gets dimmer as you rev up the engine, then you most likely have a problem with the alternator. If it gets brighter, then the battery is most likely bad.

That's all well and good, but just exactly what does all that mean? To get a good idea, it is first necessary to understand how an alternator works. You don't need an engineering degree, just a basic understanding of the general principles. Figure 1, below, is a block diagram, or a "functional" diagram, of an alternator, and its connections to the remainder of the automobile electrical system. Following the figure is a description of the various components that make up an alternator, and a description of how each operates to keep the battery charged in your car.

ALTERNATOR ROTOR

We'll start our tour of the alternator where it all starts in the alternator itself - at the alternator rotor. The rotor consists of a coil of wire wrapped around an iron core. Current through the wire coil - called "field" current - produces a magnetic field around the core. The strength of the field current determines the strength of the magnetic field. The field current is D/C, or direct current. In other words, the current flows in one direction only, and is supplied to the wire coil by a set of brushes and slip rings. The magnetic field produced has, as any magnet, a north and a south pole. The rotor is driven by the alternator pulley, rotating as the engine runs, hence the name "rotor."

STATOR

Surrounding the rotor is another set of coils, three in number, called the stator. The stator is fixed to the shell of the alternator, and does not turn. As the rotor turns within the stator windings, the magnetic field of the rotor sweeps through the stator windings, producing an electrical current in the windings. Because of the rotation of the rotor, an alternating current is produced. As, for example, the north pole of the magnetic field approaches one of the stator windings, there is little coupling taking place, and a weak current is produced, As the rotation continues, the magnetic field moves to the center of the winding, where maximum coupling takes place, and the induced current is at its peak. As the rotation continues to the point that the magnetic field is leaving the stator winding, the induced current is small. By this time, the south pole is approaching the winding, producing a weak current in the opposite direction. As this continues, the current produced in each winding plotted against the angle of rotation of the rotor has the form shown in figure 2. The three stator windings are spaced inside the alternator 120 degrees apart, producing three separate sets, or "phases," of output voltages, spaced 120 degrees apart, as shown in figure 3.

OUTPUT DIODES

A/C voltage is of little use in a D/C system, such as used in an automobile, so it has to be converted to D/C before it can be used. This conversion to D/C takes place in the "output diodes" and in the "diode trio." Diodes have the property of allowing current to flow in only one direction, while blocking current flow in the other direction. The output diodes consist of six diodes, one pair for each winding. One of the pair is for the negative half cycle, and the other for the positive half cycle. As a result of this diode rectification, the output of the alternator looks as shown in figure 4.

Surprisingly enough, the output of the alternator is not a pure D/C as one might expect, but a pulsating D/C. Because there are three windings, each with a positive and a negative half, by the time the voltage is passed through the diodes, there are six pulsations for each rotation of the rotor. This is close enough to D/C for most automotive components. Critical components, such as radios, have their own internal filtering circuits to further smooth out the waveform to a purer D/C.

DIODE TRIO

The diode trio consists, as the name suggests, of three diodes, one per phase, which provides field current to the alternator regulator. This output will be discussed in more detail later in the "field current supply" section.

REGULATOR

The regulator has two inputs and one output. The inputs are the field current supply and the control voltage input, and the output is the field current to the rotor. The regulator uses the control voltage input to control the amount of field current input that is allow to pass through to the rotor winding. If the battery voltage drops, the regulator senses this, by means of the connection to the battery, and allows more of the field current input to reach the rotor, which increases the magnetic field strength, which ultimately increases the voltage output of the alternator. Conversely, if the battery voltage goes up, less field current goes through the rotor windings, and the output voltage is reduced.

FIELD CURRENT SUPPLY

Field current supply is provided from two different sources - from the alternator itself, via the diode trio, and from the battery, via the alternator warning lamp. When you first get in the car and turn the key on, the engine is not running and the alternator is not spinning. At this time, the voltage/current source for the field current is from the battery, through the ignition switch, and through the warning lamp. After the engine is started, and the alternator is up to speed, the output of the diode trio is fed back to the regulator, and serves as a source of current for the field current. At this time, the alternator is self sustaining, and the battery is no longer needed to power the automobiles electrical system WARNING!!! This is theoretical only - in actual practice, the voltage surges resulting from disconnecting the battery can seriously damage the regulator circuitry. All alternator manufacturers strongly advise NOT doing this! This test will not prove the functionality of the alternator anyway, as the engine may still run with a weak alternator output.

WARNING LAMP

This brings us back full circle to the starting point - the alternator warning lamp. As can be seen from figure 5, a schematic for an actual alternator, there is a path to ground from the field current supply input [1] to the regulator. As a result, when the key is turned on, current flows through the warning lamp, through the resisters, transistors, and field coil, and then to ground, causing the lamp to illuminate. Once the alternator is at full output, voltage from the diode trio, also applied to [1], equals the battery voltage. At this time, with 12 volts on both sides, the lamp is out.

If the alternator should fail, voltage from the diode trio would drop, and once again the lamp would light from the battery voltage. If the alternator output is only a little low, the lamp will be dimly lit. If the alternator fails completely, and the output voltage goes to zero, the lamp will be lit at full brilliance. Conversely, if the battery should fail, and the battery voltage drops, with the output voltage of the alternator on one side and the low battery voltage on the other, the lamp will also light.

As stated earlier, if the light grows dimmer as the engine is revved up, it is because the alternator voltage is rising with the RPM, producing more voltage on the alternator side of the lamp. The closer the output voltage gets to the battery voltage, the dimmer the bulb becomes. By the same way, if the light gets brighter with increasing RPM, it is because as the alternator voltage increases, it is getting higher than the battery voltage. The higher the voltage with respect to the battery voltage, the greater the voltage difference across the lamp, and the brighter it gets.

SUMMATION

In summary, then, we can say that field current through the rotor coils produces a magnetic field, which is coupled over to the stator coils, producing an AC voltage. This AC voltage is converted by the output diodes into pulsating DC voltage, which charges the battery.

The field current is supplied from either the battery, via the warning lamp, or from the diode trio. The amount of field current allowed to pass through the regulator to the rotor, or field coil, is controlled by the voltage feedback from the battery.

And there you have it - the complete operation of an alternator in a nutshell. The next time you see the little red light, you will know exactly what it is trying to tell you.

Heating System (Cooling system 11)

You may have heard the advice that if you car is overheating, open all the windows and run the heater with the fan going at full blast. This is because the heating system is actually a secondary cooling system that mirrors the main cooling system on your car.

Heater plumbing

The heater core, which is located in the dashboard of your car, is really a small radiator. The heater fan blows air through the heater core and into the passenger compartment of your car.

A heater core looks like a small radiator.

The heater core draws its hot coolant from the cylinder head and returns it to the pump -- so the heater works regardless of whether the thermostat is open or closed.

For more information on car cooling systems and related topics, check out the links on the next page.

Fan (Cooling system 10)

Like the thermostat, the cooling fan has to be controlled so that it allows the engine to maintain a constant temperature.

Front-wheel drive cars have electric fans because the engine is usually mounted transversely, meaning the output of the engine points toward the side of the car. The fans are controlled either with a thermostatic switch or by the engine computer, and they turn on when the temperature of the coolant goes above a set point. They turn back off when the temperature drops below that point.

Cooling fan

Rear-wheel drive cars with longitudinal engines usually have engine-driven cooling fans. These fans have a thermostatically controlled viscous clutch. This clutch is positioned at the hub of the fan, in the airflow coming through the radiator. This special viscous clutch is much like the viscous couplingsometimes found in all-wheel drive cars.

Thermostat (Cooling system 9)

The thermostat's main job is to allow the engine to heat up quickly, and then to keep the engine at a constant temperature. It does this by regulating the amount of water that goes through the radiator. At low temperatures, the outlet to the radiator is completely blocked -- all of the coolant is recirculated back through the engine.

Once the temperature of the coolant rises to between 180 and 195 F (82 - 91 C), the thermostat starts to open, allowing fluid to flow through the radiator. By the time the coolant reaches 200 to 218 F (93 - 103 C), the thermostat is open all the way.

The open and closed positions of a thermostat

If you ever have the chance to test one, a thermostat is an amazing thing to watch because what it does seems impossible. You can put one in a pot of boiling water on the stove. As it heats up, its valve opens about an inch, apparently by magic! If you'd like to try this yourself, go to a car parts store and buy one for a couple of bucks.

The secret of the thermostat lies in the small cylinder located on the engine-side of the device. This cylinder is filled with a wax that begins to melt at around 180 F (different thermostats open at different temperatures, but 180 F is a common one). A rod connected to the valve presses into this wax. When the wax melts, it expands significantly, pushing the rod out of the cylinder and opening the valve. If you have read How Thermometers Work and done the experiment with the bottle and the straw, you have seen this process in action -- the wax just expands a good bit more because it is changing from a solid to a liquid in addition to expanding from the heat.

This same technique is used in automatic openers for greenhouse vents and skylights. In these devices, the wax melts at a lower temperature.

Pressure Cap (Cooling system 8)

The radiator cap actually increases the boiling point of your coolant by about 45 F (25 C). How does this simple cap do this? The same way a pressure cooker increases the boiling temperature of water.

The cap is actually a pressure release valve, and on cars it is usually set to 15 psi. The boiling point of water increases when the water is placed under pressure.

When the fluid in the cooling system heats up, it expands, causing the pressure to build up. The cap is the only place where this pressure can escape, so the setting of the spring on the cap determines the maximum pressure in the cooling system. When the pressure reaches 15 psi, the pressure pushes the valve open, allowing coolant to escape from the cooling system. This coolant flows through the overflow tube into the bottom of the overflow tank. This arrangement keeps air out of the system. When the radiator cools back down, a vacuum is created in the cooling system that pulls open another spring loaded valve, sucking water back in from the bottom of the overflow tank to replace the water that was expelled.

Radiator (Cooling system 7)

A radiator is a type of heat exchanger. It is designed to transfer heat from the hot coolant that flows through it to the air blown through it by the fan.

Most modern cars use aluminum radiators. These radiators are made by brazing thin aluminum fins to flattened aluminum tubes. The coolant flows from the inlet to the outlet through many tubes mounted in a parallel arrangement. The fins conduct the heat from the tubes and transfer it to the air flowing through the radiator.

The tubes sometimes have a type of fin inserted into them called a turbulator, which increases the turbulence of the fluid flowing through the tubes. If the fluid flowed very smoothly through the tubes, only the fluid actually touching the tubes would be cooled directly. The amount of heat transferred to the tubes from the fluid running through them depends on the difference in temperature between the tube and the fluid touching it. So if the fluid that is in contact with the tube cools down quickly, less heat will be transferred. By creating turbulence inside the tube, all of the fluid mixes together, keeping the temperature of the fluid touching the tubes up so that more heat can be extracted, and all of the fluid inside the tube is used effectively.

Radiators usually have a tank on each side, and inside the tank is a transmission cooler. In the picture above, you can see the inlet and outlet where the oil from the transmission enters the cooler. The transmission cooler is like a radiator within a radiator, except instead of exchanging heat with the air, the oil exchanges heat with the coolant in the radiator.

source http://auto.howstuffworks.com

Engine (Cooling system 6)

The engine block and cylinder head have many passageways cast or mach ined in them to allow for fluid flow. These passageways direct the coolant to the most critical areas of the engine.

Temperatures in the combustion chamber of the engine can reach 4,500 F (2,500 C), so cooling the area around the cylinders is critical. Areas around the exhaust valves are especially crucial, and almost all of the space inside the cylinder head around the valves that is not needed for structure is filled with coolant. If the engine goes without cooling for very long, it can seize. When this happens, the metal has actually gotten hot enough for the piston to weld itself to the cylinder. This usually means the complete destruction of the engine.

One interesting way to reduce the demands on the cooling system is to reduce the amount of heat that is transferred from the combustion chamber to the metal parts of the engine. Some engines do this by coating the inside of the top of the cylinder head with a thin layer of ceramic. Ceramic is a poor conductor of heat, so less heat is conducted through to the metal and more passes out of the exhaust.

 

source: http://auto.howstuffworks.com

Water pump (cooling system 5)

A water pump is an important part of the engine cooling system. It provides circulation of the engine coolant (antifreeze) through the cooling system (see the top picture).

A water pump pushes the coolant through the passages (water jackets) in the engine cylinder block and cylinder head and then out into the radiator. This helps to keep the engine from overheating; the hot coolant passes through the radiator where it cools down and then returns back to the engine.

A water pump is usually driven by the engine through the drive belt. Sometimes it's driven by a timing belt. A water pump consists of the housing with the shaft rotating on the bearing pressed inside.

At the outer side there is a pulley mounted on the shaft. At the inner side there is a seal to keep the coolant from leaking out and the impeller that acts like a centrifugal pump (see the lower picture).

Fluid (Cooling System 4)

Cars operate in a wide variety of temperatures, from well below freezing to we ll over 100 F (38 C). So whatever fluid is used to cool the engine has to have a very low freezing point, a high boiling point, and it has to have the capacity to hold a lot of heat.

Water is one of the most effective fluids for holding heat, but water freezes at too high a temperature to be used in car engines. The fluid that most cars use is a mixture of water and ethylene glycol (C₂H₆O₂), also known as antifreeze. By adding ethylene glycol to water, the boiling and freezing points are improved significantly.

	Pure Water	50/50 C2H6O2/Water	70/30 C2H6O2/Water
Freezing Point	0 C / 32 F	-37 C / -35 F	-55 C / -67 F
Boiling Point	100 C / 212 F	106 C / 223 F	113 C / 235 F

The temperature of the coolant can sometimes reach 250 to 275 F (121 to 135 C). Even with ethylene glycol added, these temperatures would boil the coolant, so something additional must be done to raise its boiling point.

The cooling system uses pressure to further raise the boiling point of the coolant. Just as the boiling temperature of water is higher in a pressure cooker, the boiling temperature of coolant is higher if you pressurize the system. Most cars have a pressure limit of 14 to 15 pounds per square inch (psi), which raises the boiling point another 45 F (25 C) so the coolant can withstand the high temperatures.

Antifreeze also contains additives to resist corrosion.

source: http://www.howstuffworks.com

Plumbing (Cooling System 3)

The cooling system in your car has a lot of plumbing. We'll start at the pump and work our way through the system, and in the next sections we'll talk about each part of the system in more detail.

The pump sends the fluid into the engine block, where it makes its way through passages in the engine around the cylinders. Then it returns through the cylinder head of the engine. The thermostat is located where the fluid leaves the engine. The plumbing around the thermostat sends the fluid back to the pump directly if the thermostat is closed. If it is open, the fluid goes through the radiator first and then back to the pump.

There is also a separate circuit for the heating system. This circuit takes fluid from the cylinder head and passes it through a heater core and then back to the pump.

On cars with automatic transmissions, there is normally also a separate circuit for cooling the transmission fluid built into the radiator. The oil from the transmission is pumped by the transmission through a second heat exchanger inside the radiator.

source: http://auto.howstuffworks.com

The Basics of Car Cooling Systems (Cooling System 2)

Inside your car's engine, fuel is constantly burning. A lot of the heat from this combustion goes right out the exhaust system, but some of it soaks into the engine, heating it up. The engine runs best when its coolant is about 200 degrees Fahrenheit (93 degrees Celsius). At this temperature:

• The combustion chamber is hot enough to completely vaporize the fuel, providing better combustion and reducing emissions.
• The oil used to lubricate the engine has a lower viscosity (it is thinner), so the engine parts move more freely and the engine wastes less power moving its own components around.
• Metal parts wear less.

There are two types of cooling systems found on cars: liquid-cooled and air-cooled.

Liquid Cooling

The cooling system on liquid-cooled cars circulates a fluid through pipes and passageways in the engine. As this liquid passes through the hot engine it absorbs heat, cooling the engine. After the fluid leaves the engine, it passes through a heat exchanger, or radiator, which transfers the heat from the fluid to the air blowing through the exchanger.

Air Cooling

Some older cars, and very few modern cars, are air-cooled. Instead of circulating fluid through the engine, the engine block is covered in aluminum fins that conduct the heat away from the cylinder. A powerful fan forces air over these fins, which cools the engine by transferring the heat to the air.

source: http://auto.howstuffworks.com

How Car Cooling Systems Work (Cooling System 1)

Although gasoline engines have improved a lot, they are still not very efficient at turning chemical energy into mechanical power. Most of the energy in the gasoline (perhaps 7 0%) is converted into heat, and it is the job of the cooling system to take care of that heat. In fact, the cooling system on a car driving down the freeway dissipates enough heat to heat two average-sized houses! The primary job of the cooling system is to keep the engine from overheating by transferring this heat to the air, but the cooling system also has several other important jobs.

The engine in your car runs best at a fairly high temperature. When the engine is cold, components wear out faster, and the engine is less efficient and emits more pollution. So another important job of the cooling system is to allow the engine to heat up as quickly as possible, and then to keep the engine at a constant temperature.

source: http://auto.howstuffworks.com

Car Cooling System

An efficient cooling system is very essential in order to protect the engine from overheating. Use good quality coolant for your car engine. The coolant level should be checked at least once a fortnight and preferably at more frequent intervals during summers.

Special attention should be given to the pressure cap over the radiator. When the coolant reaches very high temperature, it forces its way through a valve in the pressure cap and the overflow is then collected into coolant reservoir. When the engine is cool, the vacuum created in the radiator draws the overflow back. If the pressure cap is defective, the coolant evaporates through the pressure cap when it reaches high temperature, instead of flowing into the coolant reservoir. This reduces the level of coolant and can harm the engine.

Cooling system hoses should be checked regularly, especially before summer. Any hose that is cracked, and feels hard or spongy when squeezed should be replaced immediately. Ensure that the fan belt is working properly since it plays a vital part in cooling the engine. Get the cooling system serviced at the onset of the summer.

Oil Change Tech Tips

• Drain the oil while it is hot. Contaminants will be in suspension and drain more easily from the engine.

• Always replace the filter when changing the oil

• Wipe some oil on the filter gasket so the seal won't stick or tear.

• Hand tighten the filter about 1/2 to 3/4 of a turn after the gasket makes contact. Over-tightening may damage the threads or gasket, and make the filter difficult to remove the next time the oil is changed. Under-tightening may allow the filter to work loose and leak.

• If the oil is badly contaminated or sludged, the crankcase should be cleaned and flushed before the engine is refilled with oil.

• Always check the oil level after refilling the crankcase. Start the engine, then shut it off and check the oil level after several minutes. It should be at the full mark on the dipstick. Most engine hold about four quarts of oil, plus half a pint to almost a quart for the filter (depending on the size of the filter). Overfilling can cause oil foaming and leaks. Under-filling may cause a loss of oil pressure and engine damage!

• Dispose of your old used oil properly. Save it in a container and take it to an auto parts store or other facility that recycles oil. Do NOT dump it on the ground, down a storm sewer or anyplace else where it can contaminate ground water.

Why oil needs to be changed

Regardless of an oil's API service rating or additive package, all motor oils eventually wear out and have to be changed (actually, it's the additives that wear out more so than the oil). As the miles add up, motor oil loses viscosity and gets dirty. The oil no longer has the same viscosity range it had when it was new, and it contains a lot of gunk (moisture and acids from combustion blowby, soot, dirt and particles of metal from normal wear). You can't really tell much about the condition of the oil by its appearance alone because most oil turns dark brown or black after a few hundred miles of use.

The oil filter will trap most of the solid contaminants, and the Positive Crankcase Ventilation (PCV) system will siphon off most of the moisture and blowby vapors -- if the engine gets hot enough and runs long enough to boil the contaminants out of the oil. Even so, after several thousand miles of driving many of the essential additives in the oil that control viscosity, oxidation, wear and corrosion are badly depleted. At this point, the oil begins to break down and provides much less lubrication and protection than when it was new. If the oil is not changed, the oil may start to gel or form engine-damaging varnish and sludge deposits -- and eventually cause the engine to fail!

Oil life depends on many factors including driving conditions (speed, load, idle time, etc.), environmental factors (temperature, humidity, airborne dirt), and engine wear. As a general rule, most experts still recommend changing the oil and filter every 3,000 miles or six months, which ever comes first. Why? Because this provides the best all-round protection for the average driver.

EXTENDED OIL CHANGE INTERVALS

In recent years, many vehicle manufacturers have extended their recommended oil change intervals to reduce maintenance costs for the vehicle owner -- and have run into trouble. The Center for Auto Safety (www.autosafety.org) has logged over a thousand complaints about oil sludging problems from motorists who thought they were following the service intervals recommended in their owners manuals but ended up with a crankcase full of sludge.

Extended oil change intervals of 7,500 or 10,000 miles or more are based on ideal operating conditions, not the type of short trip, stop and go driving that is typical for many motorists. Consequently, most drivers should follow a "severe" service maintenance schedule rather than a "normal" service schedule to protect their engines.

Severe service includes:
* Most trips are less than 4 miles.
* Most trips are less than 10 miles when outside temperatures remain below freezing.
* Prolonged high speed driving during hot weather.
* Idling for extended periods and continued low speed operation (as when driving in stop-and-go traffic).
* Towing a trailer.
* Driving in dusty or heavily polluted areas.

Some engines, such as diesels, suffer more blowby than others and typically require more frequent oil and filter changes. For most passenger car and light truck diesels, the oil should be changed every 3,000 miles without exception -- especially in turbo diesels.

Turbocharged gasoline engines also require more frequent oil changes because of the high temperatures inside the turbo that can oxidize oil. A 3,000 mile oil change interval is also recommended for all turbocharged gasoline engines.

OIL REMINDER LIGHTS

General Motors, BMW and some of the other luxury brands have done away with recommended oil change intervals altogether and now use an "oil reminder" light to signal the driver when an oil change is needed. Some technicians now refer to this as the "Replace Engine Soon" light because of the sludging problems that have resulted from extending oil change intervals too far. The oil reminder systems estimate oil life based on engine running time, miles driven, ambient temperature, coolant temperature and other operating conditions.

On some of these vehicles, the light may not come on until 10,000 miles or higher! But keep in mind that most of these engines are factory-filled with higher quality "synthetic" oil -- so be sure to replace same with same when the oil on these engines is changed.

OIL SENSORS & OIL ANALYSIS

One of the arguments against changing oil at specific mileage or time intervals is that the oil may still be good. As long as the additive levels in the oil are adequate and the oil is not oxidizing, breaking down or contaminated with fuel or coolant, there's no need to change it. Oil reminder lights are better than mileage/time intervals in this respect, but the light is still     a guesstimate that may or may not be accurate. The only way to know for sure when the oil really needs to be changed is to test it. A sample of oil can be sent to a lab for analysis, and the report can be used to establish a change interval that reduces unnecessary maintenance. Many fleets use oil analysis to dermine oil change intervals, but for the average motorist, oil analysis is too expensive and inconvenient. The cost of the oil analysis is almost as much as an oil change.

The best approach is to use a sensor to measure the condition of the oil. A new oil monitor sensor called Intellistick is now available for this purpose. The sensor replaces the dipstick, and uses a bluetooth transponder to broadcast the condition of the oil to a laptop computer PDA or even a bluetooth enabled call phone.

SYNTHETICS

Synthetic oils are oils that are refined to a much higher degree than ordinary oils. Synthetic oils are premium oils that generally have greater viscosity stability, lower pour points and can withstand higher operating temperatures. Synthetic oils improve cold starting, reduce friction, reduce oil consumption and improve fuel economy and performance -- but they typically cost about three times as much as regular motor oil.

Some suppliers of synthetic motor oils say the higher cost of the premium quality oil can be offset by extending oil change intervals. But this would depend on the operating conditions, age and condition of the engine.

Synthetic oils are a good upgrade for most engines, but are not recommended for breaking-in newly rebuilt engines.

BLENDS & SPECIALTY OILS

For motorists who want the benefits of a synthetic oil in a less expensive product, there are "synthetic blends" that mix 20 to 25% synthetic oil with conventional oil. Blends cost about a dollar a quart more than ordinary oil, and provide many (but not all) of the benefits of a full synthetic.

There are also oils that have special additive packages for specific applications such as large, heavy Sport Utility Vehicles (SUVs), turbocharged engines (extra anti-oxidants) and high mileage engines (extra viscosity improvers and anti-wear additives).

How to choose tires and wheels...

We know you've heard it before, but it's critical enough to bear repeating. It's also a bit daunting, too, that the tires on a vehicle are the one single link to the road surface. Think about that for a moment. You can have the most powerful engine, the most sophisticated transmission, the most elaborate super-trick suspension, and every other automotive widget known to mankind, but it all ain't worth a tinker's damn if the tires (and wheels) are subpar. In a way, it's really a bit strange but that's just how the operation of the automobile is.

Luckily, after examining the facts in the above-noted fashion, you can rest assured that tire technology is at an all-time high and it keeps getting better. In fact, it's actually quite amazing that while crummy tires can hurt a great car, great tires can do wonders for a less-than-fantastic car. In other words, there are some instances where tire technology is way beyond many of the cars on the road.

The technology that makes wheels and tires as good as they are is also what can make the subject quite intimidating. Our purpose here is to try and put a finer point on some of the basics of wheels and tires, and how to select them, too. Think of it as a wheel-and-tire primer that will provide you with some ground-floor facts when it comes time to make a replacement tire purchase or a wheel-and-tire upgrade.

For starters, there's tons of information on the sidewall of any tire and we cover that thoroughly in Sidewall Graffiti. There you'll find the full scoop on exactly what all the numbers mean.

If you've bought a vehicle new and come to the point where you need to replace the tires, there are several ways to go. Of course the easy way is get the exact size and make that came on the vehicle when it was new. Beyond that, you might consider going to a better quality tire or one that improves dry and/or wet handling that's still the same size as the OE tire. The next step would be to switch to a different wheel and the reasons for doing that are numerous. Some people merely want a different look for the wheel while using the same tires that came on the original wheels. While this might be OK if you want to make an appearance change right away, we think it's better to wait until you need new tires anyway, then upgrade to a larger diameter wheel and tire all at once.

Known as the plus sizing concept, this basically means that if you have a 15-inch wheel, plus one would be a 16-inch wheel and plus two would be a 17-inch wheel. But before we get further into wheels, we want to shed some light on what you should know when walking into a tire store to buy tires for your existing wheels. And, of course, this info also applies when you're doing a wheel upgrade, as well.

Choosing the tire that's right for you involves numerous considerations. But to make the process less scary, keep these two simple guidelines in mind when considering tires. First, know your expected needs and driving uses. This consideration is important to overall driving enjoyment and a well-run tire shop will help you determine your tire needs before you lay down any green. But be sure that you and the salesperson communicate accurately as to your true requirements. Second, find a source or store that you trust enough to recommend the type of tire that fits your needs. Remember, the salespeople don't know your needs, you have to tell them. If they're good, they'll ask you the right questions to come up with the right tire. For example, they'll know to factor in tread life, ride and handling, and driving conditions to help you determine which of these parameters are most important to you.

You might be wondering what some of the questions could be. Here's a list of what you should think about before entering a tire store.

Tread life considerations: What's your idea of how long a set of tires should last? Keep in mind that in some instances, a tire's wear rating is done through manufacturer testing and may not be the most accurate representation of a tire's true life expectancy. One way to get a handle on a tire's projected life expectancy (besides what they're warranted for, say, 40,000 miles for example) is to look at part of the UTQG (Uniform Tire Quality Grading) rating. The U.S. Department of Transportation requires each manufacturer to grade its tires under the UTQG labeling system and establish ratings for tread wear, traction and temperature resistance. These tests are conducted independently by each manufacturer following government guidelines to assign values that represent a comparison between the tested tire and a control tire. While traction and temperature resistance ratings are specific performance levels, the tread wear ratings are assigned by the manufacturers following field testing and are most accurate when comparing tires of the same brand. Tread wear receives a comparative rating based on wear rate of the tire in field testing following a government specified course. For example, a tire grade of 150 wears 50 percent longer than a tire graded 100. Actual performance of the tire can vary significantly depending on conditions, but the tire's UTQG tread life number can help you get in the ballpark as to how long a tire will really last.

Wet weather requirements: Most of us live in a climate where inclement weather is a factor at least part of the time. Clearly if you live in, say, Washington or Oregon, you'll want to look more closely at a capable wet-weather tire than if you're in Arizona or Nevada. For those of you in Snow Belt states, some kind of four-season type of tire will be the minimum you should consider if not an all-out snow tire for the winter that you swap for standard tires in the milder months.

Speed rating: Even in the plains and Western states like South Dakota, Nebraska, Idaho, Montana, New Mexico, Colorado, Wyoming, Utah, and Nevada where the rural interstate speed limit is 75 mph, how often do you think you're going to need a tire that's speed rated for anything over 150 mph? Be honest and knock down your required speed rating to, say, and H-speed rated tire that's still good for 130 mph. You'll pay less and likely not notice the difference in the real world. For reference, the most common speed ratings you'll come across on the majority of tires are shown in the chart below. Speed ratings signify the safe top speed of a tire under ideal conditions. For just about any street car, a V-rated tire will be more than adequate, unless the car will actually go faster than 150 mph. Usually, most ultra-high performance handling tires have a speed rating of at least V, so while you might want the ultimate handling of that type of tire, be aware that part of what you're paying for (the speed rating) is something you'll never use. For those who want tires that make a car really stick in the twisties, it ends up that many get the speed rating anyway, even though they don't need it. That's not a bad thing, but also be aware that tires with higher speed ratings are usually made from a softer rubber compound and generally will have shorter UTQG tread life ratings and, furthermore, will not actually last as long in the real world.

Q= 99 mph 

S= 112 mph 

T= 118 mph 

U= 124 mph 

H= 130 mph 

V= up to 149 mph 

Z= 149 mph and above 

W= 168 mph 

Y= 186 mph

Ride Quality: A low-profile tire such as a 50 or a 40-series looks great, but can be harsh over bumps or potholes when compared to a 55 or 60. In general, a lower profile tire also exposes the wheel to damage more easily. Lower profile tires also have stiffer sidewalls, which improves handling but increases rides harshness. It's all about compromise and there's no such thing as a free lunch.

Noise: Some tread designs are noisier than others and it varies significantly between tire brands and tread designs. If most of your driving is on lower-speed city streets, then this won't be much of a factor. But for highway driving, you'll want to consider your options, especially if you're driving an SUV on pavement most of the time. A good salesperson will be able to tell you which tires are quieter among those you're considering; even those of the same make that are in a different line can vary in road noise.

That's the basics on tires, now we'll move on to wheels. Tires wear out, but wheels don't, so why would you want to change wheels? For many there's no reason to, especially when you look at some of the very attractive wheels that come on many of today's cars as original equipment. The way we see it, why would you bother to change wheels on such cars as a Corvette C6, late-model Mustang GT or Shelby GT500, or the 17-inch or 18-inch sport package wheels that come on the current 3 series BMW?

But, of course, some cars have hokey wheels that need to be turned into flowerpots. As such, one of the two main reasons most people consider a wheel change is simply for looks. A better-looking wheel makes a world of difference on many cars and trucks.

Besides appearance, the plus concept is a key reason to switch wheels. Plus sizing your wheels and tires is the best way to improve both the performance and appearance of your vehicle. By using a larger diameter wheel with a lower profile tire it's possible to properly maintain the overall diameter of the tire, keeping odometer and speedometer changes negligible. By using a tire with a shorter sidewall, you gain quickness in steering response and better lateral stability. The visual appeal is obvious; most wheels look better than the sidewall of the tire, so the more wheel and less sidewall there is, the better it looks. The idea of plus sizing is illustrated in the photos that accompany this story. Pretend that the four wheels we show you are for the same car, rather than the Focus, Miata, and two 3 Series BMWs they're actually mounted on. Two of the wheels (the Miata and Focus) are 15 inches in diameter, while the BMW 323iT (a wagon) and 328i have 16- and 17-inch wheels. If a car has a 15-inch wheel, then upgrading to a 16-inch wheel would be plus one and a 17-inch wheel would be plus two. You could also say that if a car has a 17-inch wheel (such as many performance cars do) then going to an 18-inch wheel and tire would be a plus one. If the car has 15-inch wheels, the 18s would be a plus three.

Besides plus sizing, other factors should be considered before shelling out big bucks for wheels. The benefits of a good-quality alloy wheel are numerous. And, of course, many cars come with them as factory original equipment. Either way, you end up with reduced unsprung weight compared to steel wheels. This is a factor affecting a vehicle's road holding ability. Unsprung weight is the portion of a vehicle that's not supported by the suspension (i.e. wheels, tires and brakes) and therefore is most susceptible to road shock and cornering forces. By reducing unsprung weight, alloy wheels provide more precise steering input and improved cornering characteristics. The added strength of a quality alloy wheel can also reduce tire deflection in cornering. This is particularly critical in a car equipped with high performance tires where lateral forces may approach 1.0g. Better brake cooling is another benefit. The metals in alloy wheels are excellent conductors of heat and improve heat dissipation from the brakes. The risk of brake fade is also reduced under more demanding conditions such as spirited driving on a twisty mountain road. Additionally, alloy wheels can be designed to allow cool air to flow over the brake calipers and rotors. The lighter rotational weight of alloy wheels can even provide a slight increase in acceleration and fuel economy.

These days it's tough to buy truly bad wheels and tires. While some wheels are lower quality than others, as is also the case with tires, there are so many good ones out there that you will usually have several possibilities from which to choose. As we've said here, be straightforward with what you really need and factor it in with that ever-present budget consideration and you'll be well grounded when it comes to keeping your car or truck on the ground.

By Miles Cook (http://www.edmunds.com)

Future tire technology

When we drive our car, we forget that the entire weight of the vehicle rests on 4 small patches of rubber, and depending on how and where you are driving, those tiny contact points can change quite a bit. A partnership between Magneti Marelli, Brembo and Pirelli has recently formed to conquer these changes and provide the driver with real time information about how the tires are behaving on the road.

The project, named Cyber Tire, will use sensors molded into the tread of the tire and a series of transponders and

receives mounted on the vehicle. While you are driving, real time data about the topology of the road, tire pressure and air temperature will be recoded and sent to a computer to be compiled with other data.

What is Piston?

 PisoFrom wikipedia

A piston is a component of reciprocating engines, pumps and gas compressors. It is located in a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder wall.

Components of a typical, four stroke cycle, DOHC piston engine. (E) Exhaust camshaft, (I) Intake camshaft, (S) Spark plug, (V) Valves, (P) Piston, (R) Connecting rod, (C) Crankshaft, (W) Water jacket for coolant flow.

How To Read A Tire Sidewall

P-Metric (example 1) P215/65R15 95S

P = Passenger Car

215 = Section width measured in millimeters (25.4 millimetes per inch)

65 = Aspect Ratio, which means the sidewall height is 65 percent of the section width.

R = Radial Carcass Construction

15 = Rim Diameter

95 = Load Index

S = Speed Rating - View Speed Rating Chart Below

A. Passenger car tire.

B. Width of tire diameter.

C. Ratio of height to width.

D. Radial.

E. Diameter of wheel in inches.

F. Load index & speed symbol

G. U.S. DOT safety standard code.

H. Max. cold inflation & load limit.

I. Treadwear, traction and temperature grades.

J. Tire ply composition and materials used.

The image below breaks down all the different components that make up the basic tire from the outer tread into the inner bead wires.

Engine Lubrication System

Motor oil does more than just lubricate an engine. It also forms a film on bearing surfaces that lifts and separates moving parts so they don't touch to reduce friction and wear. The oil film also acts like a shock absorber to cushion reciprocating and rotating parts. Oil also serves as a coolant for critical engine parts such as the crankshaft bearings and valve-train. Oil also helps prevent rust and corrosion inside the engine, and helps keep surfaces clean by dissolving and carrying away dirt and varnish deposits.

UNDERSTANDING VISCOSITY

"Viscosity" refers to how easily oil pours at a specified temperature. Thinner oils have a water-like consistency and pour more easily at low temperatures than heavier, thicker oils that have a more honey-like consistency. Thin is good for easier cold weather starting and reducing friction, while thick is better for maintaining film strength and oil pressure at high temperatures and loads.

The viscosity rating of a motor oil is determined in a laboratory by a Society of Automotive Engineers (SAE) test procedure. The viscosity of the oil is measured and given a number, which some people also refer to as the "weight" (thickness) of the oil. The lower the viscosity rating or weight, the thinner the oil. The higher the viscosity rating, the thicker the oil.

Viscosity ratings for commonly used motor oils typically range from 0 up to 50. A "W" after the number stands for "Winter" grade oil, and represents the oil's viscosity at zero degrees F.

Low viscosity motor oils that pour easily at low temperatures typically have a "5W" or "10W" rating. There are also 15W and 20W grade motor oils.

Higher viscosity motor oils that are thicker and better suited for high temperature operation typically have an SAE 30, 40 or even 50 grade rating.

These numbers, by the way, are for "single" or "straight" weight oils. Such oils are no longer used in late model automotive engines but may be required for use in some vintage and antique engines. Straight SAE 30 oil is often specified for small air-cooled engines in lawnmowers, garden tractors, portable generators and gas-powered chain saws.

MULTI-VISCOSITY OILS

Most modern motor oils are formulated from various grades of oil so the oil will have the best characteristics of both thick and thin viscosity oils. Multi-viscosity oils flow well at low temperature for easier starting yet retain enough thickness and film strength at high temperature to provide adequate film strength and lubrication.

A thin oil such as a straight 10W or even a 20W oil designed for cold weather use would probably not provide adequate lubrication for hot weather, high speed driving. Likewise, a thicker high temperature oil such as SAE 30 or 40 would probably become so stiff at sub-zero temperatures the engine might not crank fast enough to start.

Multi-viscosity grade oils have a wide viscosity range which is indicated by a two-number rating. Popular multi-viscosity grades today include 5W-20, 5W-30, 10W-30, 10W-40 and 20W-50. The first number with the "W" refers to the oil's cold temperature viscosity, while the second number refers to its high temperature viscosity.

WHICH VISCOSITY TO USE?

Most vehicle manufacturers today specify 5W-30 or 10W-30 motor oil for year-round driving. Some also specify 5W-20. Always refer to the vehicle owners manual for specific oil viscosity recommendations, or markings on the oil filler cap or dipstick.

As a rule, overhead cam (OHC) engines typically require thinner oils such as 5W-30 or 5W-20 to speed lubrication of the overhead cam(s) and valve-train when the engine is first started. Pushrod engines, by comparison, can use either 5W-30, 10W-30 or 10W-40.

As mileage adds up and internal engine wear increases bearing clearances, it may be wise to switch to a slightly higher viscosity rating to prolong engine life, reduce noise and oil consumption. For example, if an engine originally factory-filled with 5W-30 now has 90,000 miles on it, switching to a 10W-30 oil may provide better lubrication and protection.

For sustained high temperature, high load operation, an even heavier oil may be used in some situations. Some racing engines use 20W-50, but this would only be recommended for an engine with increased bearing clearances. Increasing the viscosity of the oil also increases drag and friction, which can sap horsepower from the crankshaft. That's why 20W-50 racing oil would not be the best choice for everyday driving or cold weather operation for most vehicles.

The latest trend in racing is to run tighter bearing clearances and use thinner oils such as 5W-30 or 5W-20 to reduce friction and drag.

What is Timing Belt/Chain?

From Wikipedia

A timing belt, timing chain or cam belt is a part of an internal combustion engine that controls the timing of the engine's valves. Some engines, like the flat-4 engine used in the VW Beetle, use timing gears. The term "timing belt" is also used for the more general case of any flat belt with integral teeth. Such belts are used for power transmission or to interchange rotary motion and linear motion, where either high loads or maintaining a specific drive ratio are important. A common non-automotive application is in linear positioning systems. Such belts have also been used in efforts to make a cleaner, lower-maintenance bicycle transmission, but have never become popular in this application.

What is Short Block?

From Wikipedia.

Short block is an automotive term describing an engine sub-assembly.

A short block is the portion of the engine block below the head gasket but above the oil pan. A flathead engine will also include the cam and valvetrain. The overhead valve style of engine will not include the aforementioned parts on the shortblock. A shortblock is usually purchased to upgrade the water jacket, piston size or bore. Assemblies typically include the crankshaft installed and balanced along with the main bearing.

A short block is considered destroyed when it either warps or cracks.

What is Cylinder head?

From Wikipedia.

In an internal combustion engine, the cylinder head sits above the cylinders and consists of a platform containing part of the combustion chamber and the location of the valves and spark plugs. In a flathead engine, the mechanical parts of the valve train are all contained within the block, and the head is essentially a flat plate of metal bolted to the top of the cylinder bank with a head gasket in between; this simplicity leads to ease of manufacture and repair, and accounts for the flathead engine's early success in production automobiles and continued success in small engines, such as lawnmowers. This design, however, requires the incoming air to flow through a convoluted path, which limits the ability of the engine to perform at higher rpm, leading to the adoption of the overhead valve head design.

In the overhead valve head, the top half of the cylinder head contains the camshaft in an overhead cam engine, or another mechanism (such as rocker arms and pushrods) to transfer rotational mechanics from the crankshaft to linear mechanics to operate the valves (pushrod engines perform this conversion at the camshaft lower in the engine and use a rod to push a rocker arm that acts on the valve). Internally the cylinder head has passages called ports for the fuel/air mixture to travel to the inlet valves from the intake manifold, for exhaust gases to travel from the exhaust valves to the exhaust manifold, and for antifreeze to cool the head and engine.

The number of cylinder heads in an engine is a function of the engine configuration. A straight engine has only one cylinder head. A V engine usually has two cylinder heads, one at each end of the V, although Volkswagen, for instance, produces a V6 called the VR6, where the angle between the cylinder banks is so narrow that it utilizes a single head. A boxer engine has two heads.

The cylinder head is key to the performance of the internal combustion engine, as the shape of the combustion chamber, inlet passages and ports (and to a lesser extent the exhaust) determines a major portion of the volumetric efficiency and compression ratio of the engine.