Mayo on underside of oil filler.

[scurbo]

Just got back after a 8 hour trip around manchester area looking at mk3 and mk4 golf gti's. The final one i looked at was a mk4, but i noticed a white residue under the oil filler cap and inside as you looked down. The car ran perfect, nothing unusual, it was a 1999 1.8gti, is this normal, so i know for next time.

[Steve_PD]

Could be the head gasket has gone 

[gtigolfthree]

Yes its water that turns oil white.

[Mr_Orange]

Can't it also show up just after a short journey too?

[gtigolfthree]

Yes but I think its just condensation that causes that.

[johnson6672]

It doeas happen if the car does lots of short journeys as the engine doesn't get hot enough to burn it off, but you really need to do pressure tests to confirm head gasket or other sinister things.

[gtigolfthree]

Yes I wouldnt diagnose a head gasket on one symptom you would need several of the following mayo as mentioned but also white oil(water in the oil), overheating, water consumption, water pressurising, loss of compression/performance etc.

[Dubbz]

yeah as said. could be a number of things that cause "mayo".
Two different brands of oil will cause that, as well as condensation, or worst case a head gasket.
What service history did it have?

[Stu-1.8T]

My 2.0 has this and it's only on 50k with full history/regular oil changes, but apparently most suffer with it.  Condensation forms as the heat cant escape from the top of the engine quickly enough. 

[Ivor Mk4 Turbo]

Money's on condensation if there were no signs of overheating.  Did the temp. guage stick on 90 deg. after a run?