Another symptom you might run into is milky oil, or oil that looks like frothy chocolate milk. This is usually the result of coolant or water mixing with the oil. This could be caused by a leaking head gasket, a leaking intake gasket, an oil cooler leak, or some other instance where coolant can leak into the crankcase and not directly into the combustion chamber. This is bad, because the oil will not be able to lubricate properly if it’s contaminated with coolant or moisture.
These leaks can be harder to track down because they are internal leaks. The best way to confront these is to start with the easy stuff and take it from there. For instance, start by removing the intake manifold and inspecting the intake gasket for leaks before going for the head gasket. Or, if you have an oil cooler, check it for leaks first before digging deeper into the engine.
One thing to note before I close this topic is that this condition can also be caused by “short tripping.” Short tripping is when the vehicle only gets driven a short distance and rarely gets up to operating temperature. This causes a buildup of condensation inside the crankcase, which can exhibit the exact same symptom of oil that looks like chocolate milk.
To address this issue, take the vehicle on a nice long drive to purge the condensation from the crankcase. If it was an internal coolant leak that caused the problem and you've completed the repair, I recommend you change the oil. I do this after just about all major engine work. Then I recommend you take the car for a long drive to make sure the repair took and the problem has been addressed. If you still see signs of coolant in the oil, change the oil again, take it for a drive and recheck. If you still have it then, you might need to keep looking for the source of the leak.