It sounds like oil is getting into the coolant. The cooler itself won't cause that. Something is allowing the oil to enter the system. In this case it is likely a head gasket.
Here is a link that explains how to check a head gasket and common symptoms. Take a look through it and see if it helps.
https://www.2carpros.com/articles/head-gasket-blown-test
Let me know what you find. Also, if you suspect it could be a head gasket, another thing to check is engine compression. A leak will lower compression in the engine.
Let me know what you find or if you have other questions. Also, if you plan to replace the gasket yourself, let me know and I'll provide the directions.
Take care,
Joe
May 18, 2020 at 8:49 AM
