What would be indicated by engine oil contaminated with coolant?

When engine oil is contaminated with coolant, it typically indicates a failure in the sealing system of the engine that allows coolant to enter the oil system. Leaking liner O-rings are a common cause of this issue because they are designed to create a seal between the engine block and the cylinder liners. If these O-rings are damaged or compromised, coolant can leak into the engine oil, resulting in contamination.

On the other hand, while cracked dry liners and cracked liner counter-bores might also lead to similar symptoms, they are less common causes of oil and coolant mixing when compared to issues with O-rings. A leaking oil cooler core could also cause some mixing of oil and coolant, but the O-rings are more directly related to the scenario of coolant reaching the oil system from the combustion area, making them the most likely cause in this situation. Thus, the presence of coolant in the engine oil strongly points to the failure of the liner O-rings.