Oil filter - what size particles??

I believe that a Canton/Mecca filter is rated for something like 8 or 9 microns; I don't think a regular oil filter will get you the 25 micron filtration you are looking for.

nate

They don't work quite like that. Reputable filter manufacturers will specify the *beta ratio* for a particular filter, which relates to the percentage of a certain size particle that will be removed on either a single pass or mutiple passes. Google the term for the full story.

Some manufacturers (eg Fleetguard) offer filters for various applications. An hydraulic oil oil filter (prefixed HF in the fleetguard system) will remove a higher percentage of smaller particles than an engine oil filter will.

Nor are they all the same. You'd probably find the Fleetguard Master Catalogue helpful.

Frantz still makes the old toilet-paper canister bypass filter that catches particles down to 0.1 microns. I had one in a '91 S-10 pickup, and that oil stayed really clean for a long time. The bypass system relies on the fact that the oil pump normally pumps twice (or maybe more) as much oil as the engine might require, with most of it relief-valved back into the sump, so a small amount is taken off at a tee at the pressure switch or transducer, run through the paper roll endwise, and then put back in the sump. Biggest hassles: a) drilling a hole in the pan for a return fitting (could maybe dump it into a rocker cover), and b) finding decently tightly-wound toilet paper with the older-style small core that fits these things. Supermarket TP just won't work anymore, with its "nice soft feel" for your wimpy, tender bum, and a huge core and loose wind to cut into the amount you get. Institutional-grade TP sometimes fits. See

All automotive pleated oil filters do that, and 20-25um may be the largest particle size commonly used for test dirt. I believe they typically remove 75-98% of such particles in a single-pass test. The premium line filters with filter material made primarily of synthetic material rather than paper are usually at the upper end: Pure One, Mobil 1, and Fram Toughguard (white, not orange or black).

Bypass filters remove the smaller particles, 5-10um better than pleated filters do, but that doesn't necessarily mean they remove as much dirt because they actually let a higher percentage of larger particles pass through. If you look inside one you'll notice it's full of openings much larger than any found in sieve filters, and bypass filters have been found to remove only about 50% of the 20-25u particles.

Ignore judgments of filters based only on their internal appearances and that don't show test results.