Common causes of vehicle smoke

GASOLINE ENGINES
Smoke Color	Diagnosis	Possible Causes
Black or Gray	Incomplete fuel combustion	Engine too cold (no repair needed) Clogged air filter Carburetor, choke, fuel injection or emission system malfunction Ignition timing off Blocked manifold
Blue	Engine oil being burned	Oil leaking into combustion chamber Worn piston rings, valves or cylinders
White	Coolant and/or water being vaporized in combustion chamber	Engine too cold (no repair needed) Head gasket leaking Cracked block or cylinder head

DIESEL ENGINES
Smoke Color	Diagnosis	Possible Causes
Black or Gray	Incomplete fuel combustion	Faulty injection system Clogged air filter Wrong grade of fuel Incorrect timing Engine overheating
Blue	Engine oil being burned or atomized	Engine oil level too high Worn piston rings, valves or cylinders
White	Fuel is not burning	Engine too cold (no repair needed) Faulty injection system Incorrect timing Engine overheating

Prevention is the key

A well-maintained vehicle should not emit visible exhaust. Preventing a vehicle from smoking often involves simple maintenance procedures.

Diesel engines don't have to smoke

Although diesel vehicles emit some smoke on acceleration, they should not smoke constantly. All vehicles, including diesels, are subject to the same smoking vehicle law as gasoline engines.