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Fan Clutch  The fan clutch is a small fluid coupling with a thermostatic device and controls a variable-speed fan. It ensures that the fan will rotate at just the right speed to keep the engine from overheating, and reduces drive to the fan when it is no longer needed. The fan clutch has a fluid coupling partly filled with silicone oil designed for just that purpose. When the temperature of the air passing through the radiator rises, the heat alerts a bimetal coil spring to "uncoil" or expand. When it expands, it allows just a little more oil to enter the fluid coupling, so the fluid coupling starts to rotate the fan. If the air coming through the radiator is cool, the opposite happens; the coil spring contracts, the oil leaves the fluid coupling and the fan slows. Slowing the fan when it is not needed reduces fuel consumption, makes less noise and saves engine power. Sometimes a flat bimetal strip spring is used instead of a coil spring; it bows out and in when the temperature rises and drops, letting oil in and out of the fluid coupling.

Fast Idle The higher speed, 1,100 to 1,500 rpm, at which an engine idles during warm-up, when first started.

Fast-Idle Cam  A cam-shaped lever on the carburetor that provides fast-idle action when the engine is cold.

Fast-Idle Screw A screw in the carburetor linkage to adjust fast-idle speed.

Feeler Blade A thin strip or blade of hardened steel, ground to an exact thickness, used to check or measure clearances between parts.

Filler Cap (Brake Fluid Reservoir Cover) The cap on the brake fluid reservoir has a hole for air, or is vented, to allow the fluid to expand and contract without creating a vacuum or causing pressure. A rubber diaphragm goes up and down with the fluid level's pressure, and keeps out any dust or moisture.

Firewall  The partition dividing the engine compartment from the passenger compartment on a car or truck.

Firing Oder  The order in which the engine cylinders fire, or deliver their power strokes, beginning with the number one cylinder.

The spark plug in each cylinder fires in a particular order, which is unique to the engine design.
 For example, the firing order for a small-block or big-block Chevy V8 or a Chrysler V8 is 1, 8, 4, 3, 6, 5, 7, 2.

Flywheel  A large, heavy iron or steel disc attached to the rear of an engine crankshaft in order to provide sufficient centrifugal force to smooth the power impulses from the cylinders

Four-Stroke Cycle  An internal-combustion engine that requires two revolutions per cylinder or four piston strokes to achieve a power stroke: internal stroke, compression stroke, power stroke, exhaust stroke. More efficient than the two-stroke-cycle engine

Frame (Chassis)  The basic structure of the vehicle is the frame and it provides a good anchor point for the suspension system. There are two types of frames; integral frames, or 'unibody', and conventional frames. A conventional frame is basically a 'one-piece' frame; or two 'one-piece' frames fastened together. These frames are extremely rigid to keep all the parts of the car in perfect alignment, which are attached to it. It is constructed of heavy steel and welded or cold riveted together. Cold riveting keeps the rivets from shrinking after they cool off. The integral, or unibody, frame is just the opposite. With this type of frame, the body parts are used to structurally strengthen the entire car, and all of the sections are welded into one piece. Sometimes the parts of the body and the suspension system are attached and reinforced. Also, some unibody frames have partial front and rear frames for attaching the engine and suspension members.

Free play  The amount of travel before any action takes place. The "looseness" in a linkage, or an assembly of parts, between the initial application of force and actual movement. For example, the distance the brake pedal moves before the pistons in the master cylinder are actuated.

Fuel Delivery System  The various components that move fuel from the gas tank to the engine. This typically includes a fuel pump, a considerable length of fuel line (hard tubing) and a fuel filter. Once the fuel reaches the engine compartment, it travels through the fuel injection system and into the engine to get burned along with air during the combustion process (or, in older or race vehicles, through one or more carburetors and into an intake manifold).

Fuel Injection   The setup that delivers fuel into an engine in virtually all new vehicles. There are several types of fuel injection systems, but most setups these days are multi-port systems, which squirt fuel individually for each cylinder. They feature fuel rails that run down each side of a V-shaped engine (or down one side of an inline engine) and fuel injectors. Older throttle body injection (TBI) systems that appeared on cars and trucks in the '80s were essentially electronically controlled carburetors, which squirted fuel into the intake manifold, rather than apportioning it to each individual cylinder. Some race cars run a similar setup today.

Fuel Injectors  The part of a fuel injection system that squirts fuel into an engine. When a vehicle has been modified for significantly enhanced airflow in the intake system, it sometimes is necessary to swap to higher-flow fuel injectors, so they can deliver sufficient fuel to maintain the ideal air/fuel ratio.

Fuel Pump  The fuel pump has three functions: to deliver enough fuel to supply the requirements of an engine under all operating conditions, to maintain enough pressure in the line between the carburetor and the pump to keep the fuel from boiling, and to prevent vapor lock. Excessive pressure causes the carburetor float needle off its seat its seat resulting in high fuel level in the float chamber, leading to high fuel consumption. Highest pressure occurs at idling speed and the lowest at top speed.

Fuel Tank  The fuel tank stores the excess fuel until it is needed for operation of the vehicle. The fuel tank has an inlet pipe and an outlet pipe. The outlet pipe has a fitting for fuel line connection and may be located in the top or in the side of the tank. The lower end is about one-half inch above the bottom of the tank so that collected sediment will not be flushed out into the carburetor. The bottom of the tank contains a drain plug so that tank may be drained and cleaned.

Fuse  An electrical device which protects a circuit against accidental

 overload. The typical fuse contains a soft piece of metal which is calibrated to melt at a predetermined current flow (expressed as amps) and break the circuit.

Fusible link A circuit protection device consisting of a conductor surrounded by heat-resistant insulation. The conductor is smaller than the wire it protects, so it acts as the weakest link in the circuit. Unlike a blown fuse, a failed fusible link must frequently be cut from the wire for replacement.


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Gap  The distance the spark must travel in jumping from the centre electrode to the side electrode in a spark plug. Also refers to the spacing between the points in a contact breaker assembly in a conventional points-type ignition, or to the distance between the reluctor or rotor and the pickup coil in an electronic ignition.

Gasket   Any thin, soft material - usually cork, cardboard, asbestos or soft metal - installed between two metal surfaces to ensure a good seal. For instance, the cylinder head gasket seals the joint between the block and the cylinder head.

Gas Turbine  An internal-combustion rotating engine with one main moving part: the rotor with pinwheel-like blades attached. Air is compressed by the first rows of blades and delivered to the combustion chambers, from which the exhaust is directed to pass the remaining blades and to generate the power. Power is extremely smooth due to the absence of explosions and reciprocating parts.

Gauge  An instrument panel display used to monitor engine conditions. A gauge with a movable pointer on a dial or a fixed scale is an analogue gauge. A gauge with a numerical readout is called a digital gauge.

Gear Oil A thick lubricant, generally with an SAE number of 80 or above, used in standard transmissions or differentials. These often contain additives, such as an EP additive, to guard against being squeezed out from between gear teeth.

Gear Shift 

1. A floor- or steering-wheel-mounted lever used to manually change gears in the transmission.
2. A linkage-type mechanism by which the gears in a transmission are engaged.

Gears Wheels with meshing teeth to transmit power between rotating shafts. When the gear wheels are of different sizes, a change in speed ratio occurs. Gears are made of hard steel.

Glasspack Muffler  An absorption muffler that uses fiberglass as a sound-deadening material.

GPH   Abbreviation for gallons per hour. A measurement commonly used to indicate the flow rate of a fuel pump. See also LPH. Engines that have been modified to produce more horsepower may require a higher-flow fuel pump, as well as an adjustable fuel pressure regulator.

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Halogen lamp A high-output, white-light lamp used as a headlight. Also known as halogen light.

Halfshaft  A rotating shaft that transmits power from the final drive unit to a drive wheel, usually when referring to a live rear axle.

Hard Pedal 

1. A loss in braking efficiency so that an excessive amount of pressure is needed to actuate brakes.
2. A condition whereby the load literally overrides the brakes. 

Harmonic Balancer  A device designed to reduce torsion or twisting vibration in the crankshaft. May be incorporated in the crankshaft pulley. Also known as a vibration damper.


1. That part of an engine that covers the top of the cylinders and pistons and usually contains the combustion chambers and valve train.
2. That part of a compressor that covers the valve plates and separates the high side from the low side of an air-conditioning system.

Head Gasket  A gasket that is used to enhance sealing between a cylinder head and an exhaust manifold or header.

Headers  A header is a different type of manifold; it is made of separate equal-length tubes.

Headlights  Headlights are mounted on the front of the car to light the road ahead during night or foggy days. They have reflectors and special lenses and are usually the sealed beam construction type, with the filament, reflector and lens fused together into an airtight unit. The most popular type of headlight is the halogen type, because it provides bright illumination. The halogen bulb is filled with pressurized gas (halogen) and can produce flying fragments if shattered. Wear protective glasses for changing a halogen lamp and always throw out the old one in the protective carton that comes with the new one.

Heat Exchanger The "heat exchanger" is a device that uses exhaust heat to aid in fuel evaporation. It usually is built into the intake manifold as an area where the hot exhaust gasses and fuel-air mixture come close to each other.

Heater Core The heater core is a smaller version of the radiator that is used to keep your toes warm when it's cold outside. It is mounted under the dashboard. Some of the hot coolant is routed through this little radiator, by more hoses. A small electric fan is also mounted there especially for the purpose of directing the heat inside the car. The principle is exactly the same as the one used in the radiator for your engine, except that the heat is released inside the car instead of outside.

Helical Gear  A gear in which the teeth are cut at an angle to the shaft. The advantage is that there are usually two teeth meshing at all times, making for smoother and quieter operation.

Hemi  Slang term for an engine with hemispherical combustion chambers which allow for larger and less shrouded valves. Used in many sports and racing cars.

Hemi-Head  A hemispherically shaped combustion chamber at the top of the engine cylinder. The hemispheric shape provides improved efficiency because the forces of the explosion are directed to the piston by the curved surface of the combustion chamber.

High-Performance Tire  A tire with serious traction capabilities, usually for both straight-line acceleration and cornering performance. Many high-performance tires feature a soft rubber tread compound, which enhances traction but can shorten the tire's lifespan. Of course, people who are in search of optimum traction usually are willing to sacrifice a bit of tire longevity, as well as some performance in rain and snow.

Hone  An abrasive tool for correcting small irregularities or differences in diameter in an engine cylinder, brake cylinder, etc.

Hood  The removable or lift-up part of an auto body that covers the engine and allows access to it.
The car's hood consists of an inner and an outer panel. The inner panel provides strength, while the outer panel is just a metal cover. The underside of the hood is often covered with a sound-absorbing material. Some high performance cars have 'hood scoops' which channel outside air directly to the air filter, which gives improved performance and efficiency. The hood release is a small lever, which is usually mounted under the dash. It is connected to the hood latch by a cable. The hood latch has a safety feature, which requires a second latch to be released before the hood will open. This is to prevent accidental opening while driving.

Horsepower (hp.)  The unit for measuring the power output of an engine. One horsepower is defined as lifting 33,000 pounds one foot per minute.

Hubcap  Often used as a synonym for wheelcover. In more literal terms, a wheelcover covers the entire wheel, while a hubcap covers only the center of the wheel, or the hub. “Dog-dish” hubcaps are popular among enthusiasts who like a sleeper look, and they often were found on police cars of the ’60s and ’70s.

Hydraulic  A mechanical operation based on incompressibility of liquids, generally oil and sometimes water, and their ability to offer resistance when being forced into a small cylinder or through an orifice, thereby transmitting an increase in applied force. Hydraulic brakes and clutches use this principle.

Hydraulic Tappet  A tappet that utilizes hydraulic pressure from the engine's lubrication system to maintain zero clearance (constant contact with both camshaft and valve stem). Automatically adjusts to variation in valve stem length. Hydraulic tappets also reduce valve noise.

Hydraulic Valve Lifter  Valve lifter using hydraulic oil pressure to operate and capable of maintaining zero clearance between metal parts. Thus, valve noise and wear are considerably reduced as are the periodic valve adjustments.

Hydroplaning  A wet-weather phenomenon in which a vehicle's tires ride upon a thin layer of water and lose contact with the road surface. Tires typically are designed with grooves or water channels to prevent hydroplaning.

Hypoid Gears  A type of differential final drive using a spiral bevel gear on the drive shaft, allowing it to be located below the center of the ring gear on the axle. This makes possible a lower floor in the car.


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The objective of this Web Page is to familiarize you with basic auto maintenance
-  in some common emergencies -
not to make you an expert in auto mechanics

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