The air filter on my M35B does not appear to be dirty but it always shows evidence of a little oil in the metallic filter element itself and the foam cover over the filter intake holes. I am assuming that this oil comes from the valve cover blow-by hose that terminates against the side of the filter.
Is there any way to get rid of that oil flow? There isn't much and it doesn't leak down into the sump or cause any other significant nuisance. But it offends my sense of order!
The engine needs a vent so it doesn't pressurize from compression that blows by the rings. All engines have some blow by. Choices are to re-ingest the oily vented air or to capture it. If you do a search or check the Knowledge base you will find that some have tapped into the intake manifold and routed the vent hose directly to the manifold bypassing the air cleaner. Another alternative is to route the vent hose down the side of the engine to a container of some sort. With this method you will have to periodically empty or replace the capture container.
John : Your breather vent from the oil pan is "piped" into the air breather. This is what is causing that oily film.
As Ken said the only other solution is to make a filter like I did and then clean it every 3/4 months. You'd be surprised how much oil my "beer can foam" filter captures!!! :wink: