NFB: Trick question: What does an oil filter filter?

[Roger in Kensington]

Okay, before the first wise guy responds with "Well, duh! Oil, of course" I'm being serious.

The engine takes in two things: Gasoline, which passes through a filter, and air, which also passes through a filter.

So what is there left for an oil filter to filter?

Contaminants in the oil resulting from combustion are at the molecular level (aren't they?) and so are too small for the filter to filter; thus the need to change oil at certain intervals as it degrades in performance.

As for the particulates that an oil filter should be able to filter, what is their source if the air and fuel filters are doing their respective jobs?

Inquiring minds want to know.

Thanks, O oleaginous gurus of grime!

[Kevin - Blown 95 TA]

Say some shmuck changes his oil and a bunch of crud falls into the valve cover hole, then the filter will save the bearings from the dirt, and say a rocker arm grinds itself up and metal splinters get in the engine, the filter might again save the engine. The filter is also important at break in for obvious reasons. But most of the time the filter just picks up very small particulates like the tiny bits of your engine that grinds up on every cold start.

[Joe 1320]

Okay, before the first wise guy responds with "Well, duh! Oil, of course" I'm being serious.

Oh well, I was going to say something......

[Ouija]

Don't forget the fact that most of our engines are as sealed as we'd like to think they are.

Minor amounts of dust can get introduced into the engine through bad seals, etc.

If cars can "eat oil" then isn't it entierly possible they they might also let in other things? Are your fittings around your PCV really as tight as you think?