Porsche 911UK Forum

Welcome to the @Porsche911UK website. Register a free account today to become a member! Sign up is quick and easy, then you can view, participate in topics and posts across the site that covers all things Porsche.

Already registered and looking to recovery your account, select 'login in' and then the 'forget your password' option.

Oil cap gunk, mayo, yellow/white residue and Head Gaskets


Well-known member
8 Nov 2008
The water-cooled 911 and Boxster/Cayman all have remote oil filler necks.

Most cars have the oil access directly into the top of the engine (assuming vertical, not boxer), generally via the rocker cover.

Because of this outlying filler tube and cap, during cold weather and especially after short journeys (that don't get to warm up these extremities) a white/creamy yellow gooey condensate emulsion of oil vapour and combustion water vapour can build up right at the end of the extended and horizontally lying oil filler neck and under the filler cap.

The remedy is to simply wipe off and drive faster and longer!

Some examples:


It is not harmful, and in normal circumstances the oil and water vapour would have been recycled into the block and sump. It is only the cul-de-sac of the oil filler neck and cold weather condensation that causes it.

In theory the gooey emulsion could too be recycled by the engine, if only you could get it back in! (it doesn't flow).

But it is easier just to wipe off.

Kitchen paper or similar (disposable J-cloth etc) can be used to remove the residue (the "mayo" shouldn't extend further than a few inches down the pipe, if it does wrap paper round a tooth brush or coat hanger etc - DON'T LOSE IT!). Do not use any old dirty rag either - you don't want any dirt/grit particles to enter the sump.

Head Gasket Failure
Having said that, this mayo can still be caused by a headgasket failure.

Firstly check the dip-stick (on vehicles without a dip-stick the sump may be carefuily dipped via the oil filler neck using a flexible plastic pipe etc) for water/emulsion contamination in the sump and also check for cross-contamination of the coolant in the header tank.

Make sure there is no water loss and the coolant is nice and clear - if the coolant has oil in it or you are mysteriously losing coolant (burnt off through cylinders as white smoke) then you have a headgasket failure.

The header tank will exhibit a dirty or oily composition - oil may be recognised by a rainbow skin on the surface. An HC (hydrocarbon) "sniff" test may be made by any competent garage to check for exhaust based contamination in the coolant.


If no water/emulsion in sump and no oil in coolant, and no coolant loss, then just cold weather/short run "mayo".

Wipe off and drive faster and longer!
That's a big relief. GT4. Thanks. Time to hit the revs!!
A reply to an old thread to simply say this forum is great!

Topped up the oil at the weekend, the 996 is a daily driver with a relatively short (12 mile) drive each way. Opened up the oil filler cap and to say I was concerned was an understatement!!! :sad:

A quick search on here revealed this thread and I was a much more pleasant person to be around 10 minutes later.

So to everyone on here that puts the effort into these useful threads and commenting on the questions from newbies - a big thank you, you know who you are :worship: :worship:
That's another email landed in GT4's inbox :grin:

New Threads

Forum statistics

Latest member