Auto Repair Dictionary
Compressed Natural Gas (CNG): A purified and pressurized version of natural gas suitable for use as
an automotive fuel. Most light-duty vehicles that can use CNG have a “bi-fuel” system that allows
operation on either gasoline or CNG.
Coolant (anti-freeze): The liquid in the engine cooling system that dissipates heat. Engine coolant
prevents freeze-up in winter, raises the boiling point in summer, and protects the cooling system from
rust and corrosion year round.
Coolant recovery reservoir: A tank that stores additional engine coolant and allows the radiator to be
completely filled at all times for maximum efficiency. As the engine warms up and the coolant expands,
excess is directed to the reservoir. As the engine cools and the coolant contracts, surplus in the reservoir
is drawn back into the radiator.
Compression ratio: The ratio between the largest and smallest possible volumes in the cylinder of an
internal-combustion engine. For example, a compression ratio of 9:1 means the piston will compressed
the air/fuel mixture into a space that is nine times smaller than the maximum cylinder volume.
Constant velocity (CV) joint: Typically used in front-wheel drive applications, constant velocity joints
are a form of universal joint that smoothes power delivery and allows the wheels to be turned for
steering.
Continuously Variable Transmission (CVT): an automatic transmission that uses two variable-
diameter pulleys and a steel belt to continuously alter its gear ratio. This provides smooth power delivery
and allows the engine to operate at the optimum speed for any given driving condition.
Control arms: Pivoting suspension components that connect the vehicle chassis to the spindle that
supports the wheel and tire assembly.
Crank: The car “cranks” when the starter motor is able to spin the engine or cause it to “turn over.” If the
car “will not crank” when you turn the ignition key, you hear either a clicking sound, or nothing at all. The
term “crank” is also used as a short form of the word crankshaft.
Crankcase (engine block): Largest assembly of an internal combustion engine. Consists of the lower
part of the engine which contains the crankshaft, connecting rods and pistons in an oil-tight housing.
Crankshaft: The central machined shaft in an internal combustion engine. The crankshaft converts the
reciprocating motion of the pistons and connecting rods into rotary motion that is directed to the
transmission and ultimately to the wheels.
Curb weight: The weight of a vehicle carrying a full tank of fuel but no passengers or cargo.
Cuts out: When an engine loses power or misfires and feels like the engine is shut off momentarily.