There is also the issue of contamination. Oil will be contaminated in three major ways. One will be through debris that comes in through the air intake. Once it makes it through the air filter, it ends up in your oil. Once in your oil, it starts damaging your engine.
The second source of contamination will be metal shavings from the inside of your engine. The lesser the quality of the oil, the higher percentage of these shavings because there will be more metal to metal contact inside the engine.
The third source of contamination will be from combustion by- products. Combustion by-products will generally raise the acidity of your oil, which causes corrosion in your engine. In addition, they will be left behind as the engine oil burns off and will collect on the inside of your engine as deposits. To maintain the viability of your oil as well as protection of the engine, the contaminants have to be removed/neutralized.
One of the best ways to help with this process is to keep most of the contaminants from ever getting inside the engine in the first place. That's where your air filter comes in. Conventional paper air filters are pretty worthless. How many times have you removed your air filter for replacement only to find that you could write your name in the dust that collected around the air intake? That's just the stuff that was left behind. Imagine the amount that actually ended up inside the engine.
Part of the problem is that traditional paper air filters do not fit all that snugly in the air intake compartment. They've improved, but they're still not great. More importantly, though, they let way too much debris shoot right through the filter element itself. As a side-note, they do not provide for very good air flow either.
You see, as a compromise to allow enough air flow for your engine to run "properly", surface type air filtration media have to allow certain sized particles to flow through. If they made the filtration media any more tightly woven, not enough air would pass through quickly enough to keep your vehicle running.
As a result, most paper air filters won't catch anything smaller than about 20 to 40 microns with any real efficiency. In most cases, the more expensive the filter, the lower the micron level of filtration - and the lower the better, of course.
20 to 40 microns is pretty small. A human hair is about 100 microns in diameter. The problem is that 60% of engine wear is caused by particles between 5 and 20 microns (most likely because there is so much more of it). If you don't keep that stuff out, it'll eat away at your engine.
Consider an alternative air filtration device which is more like a sponge (actually, it's foam). Because foam is "squishy" it can be made slightly larger than the air intake compartment so that when installed it fits very snug with no room for air to by-pass the filtration unit.
In addition, it has millions of "tiny" channels through which air can flow, but these channels are not straight channels. They twist and turn through the filtration media. Air can pass through easily because these "tiny" channels are actually much larger than the channels through the paper filter we just discussed. This is possible because the paper filter only has one chance to get the dirt. This foam media has multiple opportunities to catch the dirt.
You see, as the air travels through these winding channels, it can turn this way and that with ease. However, the dirt particles that the air is carrying travel in a straight line until they hit something. Obviously, at every turn, the debris within the air hits a "wall". You say, "Well, that's great, but why doesn't that dirt just bounce off the wall and keep right on going?" Good point. I tell you what, why don't we put a tacky substance in the foam so that when debris hits these "walls" it's stuck there like a fly to one of those sticky tapes. You say, "Yeah, that would work!"
Not only will it work, it will work far better than the paper air filter discussed above. Because of the depth-type nature of the foam filter AND the added tack oil, it will remove most particles larger than 5 to 10 microns. Thus, most of the harmful stuff is stopped before it ever reaches the inside of the engine.
Now, we've established that such a filtration media would seal up the intake compartment, should have better air flow, and we've established that it has more opportunities to catch the dirt, so probably less dirt makes it into the engine. The next question should be, will it hold as much dirt as the paper filter?
Well, of course it will. It's much thicker than a paper filter, and, because of the nature of the foam media, has a virtually limitless surface area over which to collect dirt. In fact, the more dirt it collects, the better the filtration (with minimal reduction in air flow). It's also much more durable than paper, so it NEVER needs to be replaced. Just wash it once a year, re- oil it and put it back in the vehicle.
---------------------------------------------------------------- Excerpted with Permission from "The Motor Oil Bible" eBook Copyright 2000 Michael Kaufman ("The Motor Oil Bible" Author) Download it from: http://www.motor-oil-bible.com ---------------------------------------------------------------- What About Additive Depletion? Part 3 - Engine Wear Particles Cause Oil Contamination Part 5