If the "mayonaise" is only on, or in the oil filler, I would bet that it is simply condensate evaporating out of your oil. Does the vehicle do lots of short runs, or is started periodically to charge battery, and never fully warms up ?
A good hot run for a few hundred miles will sometimes show condensate in the form of a creamy goo on fillers, inside of rocker covers etc. Any high and a little cooler part of an engine. Lots of British cars I have seen do it.
Pressure test the cooling system as a precaution, but the condensation of water from previous condensation events would be my bet.
Particularly if the oil in the crankcase is clean and not milky.
regards,Rod.
Last edited by walpolla; 04/11/15 09:38 AM.
