creamy residue under oil filler cap

[corex]

i have a vauxhall astra 1.6 club,got 21000 on clock with fsh,other day decided to have a look at oil level and noticed underneath filler cap it had what can only be described as "brown mayonaisse"dont have any experience of engines but thought it didn't look right,only thing is car is running fine,no overheating,no smoke or stalling,no warning lights,etc but am starting to get worried as neighbour says head gasket is blown and car could seizeup at any time,can someone please give me some advice:thanks

[Loosehead]

Your neighbour is correct, this is caused by water mixing with oil and that is a gasket gone, probably the head gasket. As it is brown it is probably only a small infiltration but it will get bigger, as it does the colour of the "mayonaise" will get lighter, at some point this will cause the engine to overheat and an engine that has over heated is never as good again. Also if your engine does overheat, a brown powdery residue will deposit itself al over your engine bay and when you come to sell it, anyone who sees that will not buy the car so you will only be able to sell it to someone who does not know that. I advise getting the gaskets checked/changed, it is most likely the head gasket but there are others.

[Tim Baxter]

Your brown mayo can be caused by innocent amounts of water in the oil.  I've had cars produce this because the breather vent to the sump or filler pipe/rocker cover had been blocked or simply not fitted due to crap design.  Get your engine pressure checked to find if your head gasket is blown.  Do you have to keep topping up your rad?  If not it's unlikely your gasket is blown.

[pjm007]

It could be a crack in the cylinder head, but hopefully not. The most likely and common explanation would be the head gasket. Have you noticed the car over-heating at all ? If so, the head could have warped/distorted which will require skimming, this can be expensive as it involves alot of labour.

[Cockney_si]

Sounds like it's just some damp got in under the filler cap, probably due to condensation in the damp weather.

Check your radiator/antifreeze top up bottle for brown sludge and the dispstick may well have traces of sludge too, if this is the case the head gasket is leaking.

[KebabMeister]

When I worked with Rover cars we used to have quite a problem with this.  It was often caused by additives to the oil which meant that on short runs (i.e. engine not getting hot) condensation would form within the engine and form the mayonaise sludge.

First thing I would do is try and clean the sludge out.  If you have an airline then pressurise the breather system.  I would recommend changing the oil as well to a different brand.

Also, can you confirm that the car is used for short runs?

I would avoid changing the head gasket until you investigate this further.  It's an expensive job for something that could be as simple as condensation!

[BreenM]

yeah most sensible thing is to get the engine pressure checked.  Also worth noting , certainly on Novas I've come accross is  the filler cap to be faulty and letting in condensation etc which can give the impression of a blown cylinder head. As long as you are definitely losing no water and car seems to be driving ok then you might be lucky and there's no real problem.