There are two likely suspects here. The first is a blown head gasket which is allowing the oil and coolant to mix. Sometimes this shows up as oil in the coolant, sometimes as coolant in the oil.

It certainly sounds like it could be a blown head gasket that is allowing the car’s coolant to mix with its engine oil. A brown, oily looking fluid in the radiator is a sign that this may have ...

Q: I recently completed a 1,400-mile trip in my 2018 Cadillac XT5. Once home I took the car in for an oil change and was told that my radiator was about a quart low of coolant. The service adviser ...