Oil in the Combustion Chamber
Oil burning in the combustion chamber results in the blue-gray colored exhaust. Oil enters the chamber past the valves and piston rings. Worn valve seals allow the oil to seep into the cylinders overnight, resulting in blue colored exhaust in the morning.
Faulty valves and worn piston rings also cause blue colored exhaust. A clogged, faulty, or closed PVC valve results in excessive crankcase pressure forcing oil past the piston rings and into the chamber.
A rich fuel condition causes black-colored exhaust. Leaking fuel injectors or excessive fuel pressure result in a black-colored exhaust and a sooty tailpipe.
White-colored exhaust is the result of coolant burning in the combustion chamber. It's typically the result of a bad head gasket or warped cylinder head.
A wet cylinder compression test indicates 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 indicates 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.