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Smoke which is visible under the hood will be either blue-gray smoke from burning oil, or white steam from the cooling system. Both symptoms indicate a leak. See Fluid Leaks above.

Smoke in the exhaust indicates something getting into the combustion chamber and being burned which does not belong there. The color of the smoke identifies the contaminant.

Blue-gray smoke is from oil. Oil smoke, probably accompanied by increased oil consumption and oil residue on spark plugs, indicates that engine oil is getting past piston rings, valve guides, the cylinder head gasket, or some combination of the three. Use a compression test for diagnosis. See 3.2 Diagnostic Testing. Compression pressures in an older engine which are even, but below specifications, point to piston ring and cylinder wall wear and the need for engine overhaul or replacement. If the smoking is most obvious under high engine vacuum, such as while coasting at high RPM, and compression pressures are within specifications, leaking valve guide oil seals or valve guides are a probable cause. See 4. Cylinder Head for repair information.

Oil smoke or steam appearing suddenly in the exhaust, along with low compression pressure in one cylinder or two adjoining cylinders, is very probably due to a failed cylinder head gasket. Look also for coolant loss, oil in the radiator, or water in the oil (which turns the oil an opaque, creamy brown). See 4.8 Removing and Installing Cylinder Head for repair procedures.

Black smoke is caused by the engine getting too much fuel. See FUEL SYSTEM for more troubleshooting information.

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