Hi guys

Been checking over my motor and after removing the oil filler cap i noticed a sort of bright greeny yellow residue on the cap and tube, Was woundering if this could indicate that coolant has somehow got into the oil.
The coolant header tank and rad have no signs of oil at all. Oil from the dip stick also looks normal, and the coolant level doesn't appear to have drop but this still is a concern to me.
I'm used to standard piston motors and if i saw that green/yellow stuff on the oil cap i'd suspect a head gasket failure.

I know these motors run hot compared to piston engines and that the residue could be the a poor oil degrading in higher temperatures

 

Combustion gases seeping into the oil sump will condense out some water over time.
Just clean out the filler neck once every year or so.