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Oil problems Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Mon, 14 Oct 2002 09:55:53
In Reply to: Still trying to figure it out?, Wayne, Fri, 11 Oct 2002 21:00:50 Members do not see ads below this line. - Help Keep This Site Online - Signup |
I'm not an oil expert by any means, because I work with people that are, and understand how much I still don't know. As part of my job I deal with detecting oil failure and oil-related failures. I can tell you this much-
Oil gets contaminated by water and combustion by-products. Those combustion by-products include small carbon particles. As oil is heated, it degrades. The typical by-product of this degradation is acids. TAN, or Total Acid Number, is the measure of these acids, and increases as the oil is heated and ages. Some of the additives in oil are buffers that neutralize the acids. Over time the buffers get used up, so the acid level increases. These acids attack seals and metal surfaces. The acids don't burn or boil off.
Water in the oil can corrode metal parts. Water is also a lousy lubricator as compared to oil. Water combines with other things (like carbon particles) to clog passages. Water gets boiled out of the oil if the oil temperature gets high enough, for long enough. That's one reason why short trips are harder on cars than longer ones, because the water doesn't get a chance to boil off. Ten miles may or may not be good enough to boil off all the water. And that doesn't clear out contaminants; most won't boil off. All the high temperature does is allow the contaminants to chemically combine with the oil into more, evil compounds.
At localized hot spots in the engine, oil can turn to coke. This is of particular concern in turbocharged engines, where the turbo temps get very high. A minor problem is the turbo oil feed line coking up; the high temps can cause coke buildup on the line. If enough builds up, it'll block the line. But in most cases, a little coke builds up, but is washed away. That's good for the feed line, but bad for the rest of the engine. That coke is abrasive to bearings, and can clog things up elsewhere.
Ethyl Glycol is a component of anti-freeze, and can leak into the oil system in small amounts if there are head gasket problems. The combination with oil creates a compound which can literally gum up small passages.
Yes, oil filters do filter out particles, but not all. Most automotive oil filters trap down to about 15-20 microns, but efficiency falls off as the filters plug up (age). 20 microns may sound like pretty fine stuff, but that's about the equivalent of 800-grit sandpaper, along the lines of medium lapping compound. That will just keep floating around the engine until the oil is drained. In the meantime, it's chewing its way through bearings and races.
As bearings wear, they spall off small particles. As the bearings wear more, and the pits enlarge, the particles increase in side, getting up into the 50-100 micron range that will be captured in the filter. But the sub-20 micron particles are still being sloughed off. And even without pitting, any sliding surface (piston ring/cylinder wall) is sloughing off particles too fine to be caught by the oil filter.
There is a test of oil called JOAP which does a spectroscopic analysis of the oil. It determines the metal content in the oil to determine what parts are wearing. This works on filtered oil, so there are always fine particles in the oil.
After seeing what happens when metal and seals wear, oil gets heated, combusion by-produces leech in, I change my oil frequently. I paid too much for that engine to let that 'stuff' float around.
posted by 192.249....
, Fri, 11 Oct 2002 11:36:47, Mon, 14 Oct 2002 09:55:53 <-- Viewing This Message
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