Exhaust Color Diagnosis | White Smoke Blue Black

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Exhaust Color Diagnosis

A rich or lean fuel condition and fluids leaking into a cylinder can damage the catalytic converter and result in colored exhaust. Exhaust color can indicate a problem with the engine's combustion.

Blue/gray Exhaust

Blue/gray exhaust is an indication of oil burning in the combustion chamber. These are possible symptoms and causes:

Valve Seals: Leaking valve seals will cause blue/gray exhaust smoke.

Valve Guides: Excessive clearance between the valve stem and the valve guide allows the oil to leak past the gap into the cylinder.

Piston Rings: Worn or damaged piston rings will cause blow-by, resulting in blue/gray smoke.

Worn Cylinder Walls: Worn cylinder walls also cause blow-by, resulting in blue/gray smoke.

PCV System: A stuck closed PCV valve causes excessive crankcase pressure, resulting in blue/gray exhaust.

Black Exhaust

Black exhaust smoke is an indication of a rich fuel condition. These are possible causes:

Fuel Injectors: A leaking or dripping fuel injector will cause a rich fuel condition.

Fuel Pressure Regulator: A stuck closed fuel pressure regulator will cause a rich fuel condition.

Fuel Return: A restricted fuel return line will cause a rich fuel condition.

White Exhaust

White exhaust smoke is an indication that coolant is burning in the combustion chamber. These are possible causes:

Cylinder Head: A crack in the cylinder head (around the coolant jacket) will cause coolant to enter the combustion chamber.

Engine Block: A crack in the deck of an engine block near the coolant jacket will cause coolant to enter the combustion chamber.

Head Gasket: A damaged or blown head gasket will cause coolant to enter the combustion chamber resulting in white/gray exhaust coming from the tailpipe.Next

Leaking Valve Seals

Leaking valve seals result in blue-gray exhaust smoke. Oil is leaking past the seal and into the combustion chamber. These seals allow the intake and exhaust valves to move up and down while providing oil for lubrication. They must allow enough to lubricate the valve stem while preventing seepage into the chamber. Valve seals can become damaged in time or from sludge building on the top of the cylinder head. This results in seepage into the combustion chamber while the engine rests. The oil in the combustion chamber causes blue/gray exhaust at startup. This blue/gray exhaust will usually clear as the oil burns off in the chamber.