I seem to get a small amount of "mayo" on the oil cap after almost every trip at the moment. I recently changed the oil for Shell Helix Ultra 5w-40 fully synthetic and have since travelled Newport (South Wales) to London and back so that should have given it time to clear up any moisture. I presume it's likely to be my still reasonably short journeys and using the blowers meaning the engine takes longer to get up to temp. My coolant has gone down slightly, but on topping up to the max mark when cold I noticed some coolant had been forced out of the expansion tank, so will try to run it closer to the min mark when cold and see if the level keeps falling. Can't help worrying though as I can't visualise how that much condensation/vapour could possibly get into the engine block/oil to emulsify on the oil cap. The only entry point I can think of is the breather system which on the 1.4 mpi is just a pipe joining the throttle body air connector (after the air filter) without any kind of valve or EGR thingy to the rocker cover.

Edited 5 December, 201015 yr by anewman

As long as the mayo is confined to the oil filler cap it's fine.

Easy test. Clean mayo up after engine warmed up, and go for a long drive. If it hasn't returned all is good. If it's back after this test, suspect head gasket leaking.

Mayo after short runs is normal. Engines produce a lot of water when cold.

Ah I guess vapours must pass from combustion chamber to oil via pistons/rings, and presumably with the amount of air the engine takes in, and how much water air holds, this could easily amount to alot. Hmm.. It's interesting that the Favorit with the same engine block design hardly ever seemed to produce mayo, which was on rather high mileage and I used that on shorter journeys - although I was told newer engines tend to produce more mayo due to being made to meet european emissions regulations. Will continue to monitor anyway