Fuel in Oil Analysis

Hi to y'all,

I have a question concerning my last oil report from Blackstone (912ULS with 150hrs). They indicated that there were remains of fuel in the oil sample.

In parallel after this report I discovered now that the oil got a little colored red since the last oil change (AVGAS UL 91 is colored red in EU).

Contamination with fuel when making the oil sample can be excluded. Blackstone indicated to fly the plane before the next sample what might help to eliminate the fuel in the oil.

Did anyone else experience that? What is the technical background that fuel can be mixed with the oil (Fuel passes piston rings?)? Should I be concerned?

Thanks in advance

Michel