Car: 1997 328i 5-speed, 160k miles I check my oil every week like a good BMW owner. Lately is has been extremely cold here, hitting -15°F a couple of days. The underside of my oil cap looks like this: This happened last year about this time, and I thought I had a blown head gasket. The people over at Bimmerforums convinced me it was just moisture in the oil (since the milky yellow stuff wasn't in the oil at all) and sure enough when it got nicer out it went away. It's happening again, and I just want to know if it's going to harm anything. I thought maybe I had a PCV valve going bad but I can't find anything in my Bentley manual or online, so I don't know if my car even has one.
Rest easy, Where ever you are it's too cold ! I also think if you have a bad head gasket you would be seeing much more of that light tan colored foam (on the outer edge of the ring) all over the cap.
That looks normal to me for cold weather. Just make sure to change the oil (and not by BMWs schedule- 6k max on synthetic and 3-4k on good quality regular.) Yes, you have a crankcase breather separator under the intake, and it can cause different problems.
