A couple of weeks ago I removed the oil filler cap for a routine check after a month of neglect. Oh joy: The dreaded mayonnaise was staring up at me from the inside of the cap. Everything else inside looked fine though. I poked with a finger under the cover, but found only nice, clean oil. I have since checked the filler cap almost daily, but the mayonnaise has not returned.

Naturally, what I feared was a blown head gasket. But as the problem seems to have gone away, and as I most likely have not got a self-repairing Volvo, I am looking for alternative theories. The only one that springs to mind is that due to the cold weather we had earlier and my car doing mostly shorter trips, there could have been a certain amount of condensation under the cam cover. Does this sound reasonable? Or should I start pressure testing to confirm a gasket leak?

Erling.
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1987 240 GL 82K miles

I would guess it's more like whipped cream than mayonnaise. I live in a moderate climate. I installed a crankcase catch tank to improve oil seperation and I get it in the bottom of the tank all the time. I concluded it was airated oil.

Just condensation from this cold weather.

Change your oil a bit more and smile in satisfaction that you own a rugged car.
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Don Foster (near Cape Cod, MA)

you hit the nail on the head. short trips + cold weather = mayo. the filler cap is the coldest part of the engine.
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Kenric Tam
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'

What can you discern by peering into the oil filler hole? life's meaning itself? A car broker once told me he checks out the camshaft color through the filler hole. A reddish, shellack color suggests a run-hot cam; clean and silvery means normal operation. My 765T has the former, the always-faithful 745na has the clean cam. Is this a real indicator of engine temperature operation?
chrisinVT
244,745,765,r100RS;r80RT

Thanks! This was exactly the reply I was hoping/praying for! There was a period this winter when it was virtually raining inside the trunk; because of condensation hundreds of drops were forming under the trunk lid. Something similar must have happened in my engine.
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1987 240 GL 82K miles