Exhaust and the Combustion Chamber

Oil burning in the combustion chamber results in blue colored exhaust. Oil enters past the valves and piston rings. Worn valve seals allow oil to seep into the cylinders overnight resulting in blue colored exhaust in the morning. Bad valves and worn piston rings also cause blue colored exhaust. Oil can pass by this weak seal and into the chamber. A clogged, faulty or closed PVC valve will cause excessive crankcase pressure to develop. This pressure forces oil past the piston rings and into the cylinder.

Black colored exhaust is caused by a rich fuel condition. Leaking fuel injectors or excessive fuel pressure can result black colored exhaust at the tailpipe. White billowing exhaust is caused by coolant burning in the combustion chamber. White colored smoke is typically the result of a bad head gasket or warped cylinder head.

Engine Cylinder Cutaway

A cylinder compression test will identify if it’s a valve or the piston rings causing the blue exhaust. After locating a cylinder below specifications, the next step is to perform a wet compression test. This test will indicate whether it’s a bad valve or weak piston rings causing the smoke. An ounce or two of oil is inserted into the cylinder. The crankshaft is rotated a few times and new compression readings are taken. If the compression has increased, it’s because the weak seal between the piston rings and the cylinder wall has been filled with oil. If it has not, it is caused by a faulty valve; most likely an exhaust valve.