Ryan360

I read from a reputable oil analysis lab in Indiana that the most common engine oil contaminant is fuel followed by moisture.

Does anyone know how do these contaminants get in our aircooled engine in the first place? How common is this problem?

Steve Weiner-Rennsport Systems

Ryan,

Fuel contamination is the byproduct of combustion and it gets by the rings. Naturally, as the pistons and rings wear, this blowby increases over time and this is why we perform leakdown tests. Certain kinds of rings can minimize this.

Moisture comes from condensation as the engine cools off and both phenomenon are totally normal.

These are the main reasons why you should change oil on a regular basis,...

springer3

Burned fuel is almost all carbon dioxide and water vapor. Ergo the main contaminant in the oil is water, either condensed blow-by gas or condensed from the atmosphere. Contamination by raw fuel would take a major malfunction in the fuel system.

I recall reading a post here from a fellow who cracked open his oil drain plug regularly to discharge water that had collected in the bottom of the oil tank. I have never found liquid water, but I never use the 911 unless I plan to drive it some distance and get the oil hot enough to drive off any condensed liquids.

Indycam

On a cold start up raw gas gets onto the cylinder walls then gets past the rings .
In a hot engine a very small amount of gas will stick to the walls of the cylinder .