a little puzzled by the value of UOA's

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Oct 12, 2005
I'm a bit of a novice to this, so please forgive if this is a dumb question. I don't doubt the usefulness of UOA's to see how well an oil is holding up against viscosity breakdown and engine wear. But it seems to me that a very important property of the oil is its to keep things clean and to not allow varnish or sludge to form. Is there anything in a UOA that gives an indication of this? I ask because my previous car was a 2001 Toyota Corolla. Not a known sludger, supposedly. But from probably 50k on there was visible varnish and even some dark brown material visible on the dipstick. I wasn't great with the maintenance (too many other crises going on in my life at the time), but it did get regualr oil changes at not more than 4500 mile intervals at a Valvoline quickie place. By 120k miles, things were beginning to get serious. I think shorter intervals, or maybe synthetic oil, were called for here, but I thought that what I was doing was reasonable at the time and it easily met Toyota's requirements. Would a UOA have caught this?
Yes it probably would have. The insolubles would have been high with the interval you where doing. You would also have seen the oil thinning out quickly. What you are seeing is fairly normal with standard dino oil. One of the reason to use synthetic. With the newer SM oils this may not happen anymore but I am still not quite a believer yet. However auto-rx will return your engine to close to new with several treatments. Then synthetic can keep it that way or pray the newer SM oils will.
A couple other things that UOA's are useful for-coolant in the oil (indicating a head gasket issue) or excessive fuel dilution.
I think you're quite right, dinosauract. That is probably the biggest oil-related concern that UOAs don't address. There seems to be a consensus that synthetics will keep an engine cleaner, although it isn't all that clear whether it's really that important. There is also a general consensus that Auto-RX treatments will make more difference than synth vs dino, and will be much cheaper in most cases. There is not so much consensus on whether keeping the engine spotlessly clean is really important. I'm running my own Auto-RX trial to see if it makes any noticeable difference in my own high-mileage engine. There are many engines here that have run dino all their lives, and that still put out excellent wear numbers. In that case, any cleanliness issues related to the choice of dino oil clearly haven't actually affected engine longevity. It's not as easy to evaluate cleanliness as wear, so there is just less that can be confidently concluded about it. This is one area where fans of synthetics have a legitimate argument, I'd say. - Glenn
Cleanlines is not that easy to detect in UOA. I can analize a lousy CD oil that thins out from a 40 to a 30, ends up with <.5 TBN, and hardly any wear materials or solids. Then I put a good detergent oil like Delo and get at least two changes where the viscosity increases, wear metals and insolubles increase. By the 3rd or 4th oil change it gets reasonable. So a lack of wear metals and insolubles sometimes just means more sludge clinging to the metal for lack of detergency/dispersion. UOA is most valuable as part of a proactive maintenance program, and is useless unless it comes with a pretty good set of comentaries and interaction to understand where and how the equipment is used and what has been done to it. It should also have good comparisons to the possible, not just the "norms".
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