If you observe oil continually appearing in the radiator, what would you suspect?

When oil continually appears in the radiator, it indicates a breach between the engine oil system and the cooling system. This is most commonly caused by a leaking cylinder gasket. The cylinder head gasket serves to seal the combustion chamber, as well as the oil and coolant passages. If the gasket fails, oil can leak into the coolant passages, leading to oil being present in the radiator.

This issue can lead to serious engine problems, including overheating and oil contamination of the coolant, which can hinder proper cooling of the engine. Identifying a leaking cylinder gasket early can prevent more severe engine damage and costly repairs.

In contrast, a blocked oil filter could restrict oil flow, but it would not typically result in oil entering the coolant system. An oil overfill might create excessive pressure, but it wouldn't lead to the oil mixing with coolant in this way. Similarly, while a malfunctioning oil pump could cause oil pressure issues, it does not create a direct link that causes oil to enter the radiator. Thus, the presence of oil in the radiator is primarily associated with a failure in the cylinder head gasket.