Hey all,

New to me 2006 Cooper S that is experiencing oil/ coolant mix.

Pulled compression and it’s 145-145-150-150 ( so that is a good sign).

The car has an automatic transmission and my understanding these do not have the oil cooler like manuals that is routinely referenced here as causing this issue.

Fairly stumped what else is causing this cross-over in the coolant expansion tank. It accelerates / decelerates without smoke, timing sounds good and oil dip stick and oil fil cap are totally clean.

Open to hear others feedback here.

As always, Will take to my mechanic if a bigger issue but wanted to give it a shot first.

Thanks,

 

Possibly the previous owner put the wrong fluid in the coolant expansion tank? Could try removing it and cleaning it and refilling.

 

If you have a compressor the cheapest thing to try is to blow compressed air into each cylinder.
First, see if you get bubbles in the coolant reservoir. If you don't see any bubbles then replace the reservoir cap, leave the compressor on for a minute and then remove the cap. Did it pressurize the cooling system(you hear air or see coolant come out when you remove the cap). If so you have a blown headgasket.

If not congrats, it may just have been that previously the headgasket was blown and you need to flush your cooling system, likely several times to get the oil out.
good luck
Bruce