2007 MCS, oil changed at 5K and recently at 10K. Runs like a top, no CEL

When I changed the oil at 10K last week the old oil looked fine in the drain pan, when I checked the coolant it was bright blue as well - both looked "normal" with no evidence of cross-contamination. However, the underside of the filler cap had a thin coating of cream-colored goo the consistency of thin yogurt. Cleaned it out, and drove the car this last week. When I checked the cap this evening the same yucky film was there again.

It's been below 0 degrees F and single digit temps here and I've only been driving my car to work across town about 3 miles at top speeds of 30, so it hardly has a chance to really warm up. It seems like this stuff could be just condensate collecting at the high point in the engine and absorbing oil.

Any thoughts? Any similar experiences?

 

Not in my R53 but yes in my 330 when I run the engine for short time (15 minutes). That is water condensation mixed with oil that's why it looks creamy.
When I store my car, I run it at various rpm speed but mostly idle rpm every 2 weeks for about 20 minutes or until there is no more water condensing on the tail pipe as I don't want any water left to cause corossion of the inside exhaust pipes. After shutting the engine off, I take the oil cap off to vent water vapor until engine cools down then replace the cap.

 

It's the short trips you're taking. It doesn't allow the moisture to burn off, so you get that goo on your filler cap. Take the long way home, and it will solve the problem.

 

Thanks much, I figured that's what it was but wanted to get some sort of confirmation.

 

As was said before - Short trip with the car not heating up the engine oil enough to evaporate moisture in the oil. However, do check the dip stick. If you have a head gasket leak, the oil will have a coffee with creamer look. But like you said, the oil looked good when you replaced it.