Hi, first post. I'm not new to cars, but I want to make the best diagnosis possible. I have a 2003 C70. The oil looks like chocolate milk and I get white smoke from the exhaust.

I'm assuming head gasket, but I've read it could be the oil cooler.

How do I make the most accurate diagnosis to avoid replacing something unnecessary.

 

a few things to try: you can get a test kit to test the coolant for exhaust gas. Are you losing coolant over time? Its possible some oil foaming and white could be condensation if the car is not driven regularly or for enough miles to get a full warm up. Is your temp gauge reading normal? (a faulty thermostat could keep the engine from fully heating up to rid of any condensation). How does your coolant look - green? rusty red? oil on top? You can also send a sample of your oil to a lab like Blackstone Labs for analysis to see if the foaming is water or coolant as well.