As a mechanic with many years of experience there are only a couple of ways engine oil can enter the coolant system 1. Some idiot added oil to the coolant overflow tank or radiator. 2. A crack in between an oil gallery and a coolant passage either in the engine block or the cylinder head(s).
- Someone added oil to the coolant overflow tank or radiator.
- A crack in between an oil gallery and a coolant passage either in the engine block or the cylinder head(s).
There could be some other reasons but it has been my experience that if you have oil in the water you have a serious problem. Take my advice, drive em like you stole em and when they won't take anymore scrap em!