Intermix is not the oil cooler - now what?

[Doug427]

I had made a post a short while back that changing the oil cooler had solved the intermix problem I have in my 2002 Boxster S. I finally got to drive it on a long trip (200+ miles), and returned home to find significant amounts of oil in the coolant expansion tank. As before, there is oil in the coolant expansion tank, but absolutely zero water in the oil. I had flushed this thing to within an inch of it's life using Prestone flush, very thoroughly draining and refilling 2 more times, then another refill with distilled water and pink coolant. Given the multiple flushes and refills done I think there's zero chance that the significant amount of oil I found in the tank is residual oil from the previous issue. It is the same issue - the intermix problem is the same as it was before. I had checked the old oil cooler as I had read others had done, and I did not get bubbles from the water side to the oil side of the cooler. However, I was hopeful the issue originated with the cooler, as the cooler bolts were less than finger tight when I went to change out the cooler and of course the o-rings.

The question now is how do I proceed? At the end of the day, this is about a $7K car, give or take. It's a very nice car with 105K miles on it. It just doesn't have a lot of value - none of them do. It's just the way the market is. I'm not looking to profit from the car, but logically I can't see tossing a rebuilt engine into the car that costs as much or more as the entire car is worth. I've done a thorough search, and so much of the info is incomplete or contradictory. Best I can tell, if an intermix is not the oil cooler, it's almost always a cracked cylinder head.

If not a cracked head, what else could it be? How do I diagnose a cracked head, and which head it is? Do I need to remove the engine to check and replace a head? What are my options and anticipated costs for the various options?

I appreciate any help and direction you guys can give. Thanks.