For 1990-2009 cars

Cause | Correction
--- | ---
DEFINITION : Foamy or discolored oil or an engine oil "overfill" condition may indicate coolant entering the engine crankcase. Low coolant levels, an inoperative cooling fan, or a faulty thermostat may lead to an "over temperature" condition which may cause engine component damage. Contaminated engine oil and oil filter should be changed.

1. Inspect the oil for excessive foaming or an overfill condition. Oil diluted by coolant may not properly lubricate the crankshaft bearings and may lead to component damage. Refer to Lower Engine Noise, Regardless of Engine Speed .
2. Inspect by performing a cylinder leak-down test. During this test, excessive air bubbles within the cooling system may indicate a faulty gasket or damaged component.
3. Inspect by performing a cylinder compression test. Two cylinders "side-by-side" on the engine block with low compression may indicate a failed cylinder head gasket. Refer to Engine Compression Test .

Faulty cylinder head gasket. | Replace the head gasket and components as required. Refer to Cylinder Head Replacement .
Warped cylinder head. | Machine the cylinder head to proper flatness, if applicable, and replace the cylinder head gasket. Refer to Cylinder Head Replacement and Cylinder Head Assemble .
Cracked cylinder head. | Replace the cylinder head and gasket.
Cracked cylinder liner or engine block. | Replace the components as required.
Cylinder head or engine block porosity. | Replace the components as required.