carburetor: A device that vaporizes fuel and mixes it with air in proper quantities to suit the varying needs of the engine. Carburetors have been replaced by fuel-injection systems on most vehicles built since 1990.

catalytic converter: A pollution-control device that consumes unburned gas in the tailpipe and reduces nitrogen oxide emissions.

clutch: In a manual transmission, a device that disconnects the engine from the transmission to allow the driver to change gears and then allows the engine and transmission to resume contact and turn together at a new speed. In an automatic transmission, a clutch performs a similar function.

cold air collector box: A rectangular box that contains the air filter. It performs the same function as the air cleaner.

compression gauge: A device used to check the amount of pressure created in a cylinder when the piston is at its highest point and is squeezing the fuel/air mixture into the smallest possible space.

coolant; antifreeze: An ethylene glycol or propylene glycol solution that raises the boiling point and lowers the freezing point of the water in the cooling system, prevents rust and corrosion, and lubricates the water pump.

cylinder: A hollow, tube-shaped pipe in the engine block in which the piston rides up and down to compress the fuel/air mixture that drives the engine.

cylinder head: The part of the engine above the engine block that contains the combustion chambers and the valves. The spark plugs screw into the top or side of the cylinder head.