Thanks RSH and etsa,
Those synptoms sure are close to mine. A quick follow-up question for etsa - Did you car run rough through the entire process. Mine doesn't run rough at all, the temperature stays normal and I can't see any oil in the expansion tank.
I'm going to replace the expansion tank filler cap today. At least that will take care on one part of the puzzle.
Regarding the expansion tank, could that developed a small pressure leak (I don't see any liquid around it)? It's plastic and almost 9 years old.
Thanks again guys,