Originally Posted By: tig1
Originally Posted By: Kuato
Originally Posted By: donnyj08
Valvoline is so underrated here. Almost every UOA is fantastic.
+1!
How does a UOA tell much about the quality of an oil?
Depends upon how you define "quality of the oil" ... "Quality" is not well defined in your question.
If you are going to talk about base stocks, or other things that don't have a direct effect on wear, then it won't. Things like vis, FP etc can vary widely, and yet not directly affect wear (if at all) until they are GROSSLY out of spec.
If you are going to talk about wear metal rates, which shows how the whole system is working in concert (or perhaps in cacophony), then the UOA will let you know how the oil is performing.
Engines that have good lube system design, and don't stress the lubes much, will do well with about any lube. Think of the 4.6L Ford or the Duramax, for a couple of examples. Really does not matter what goes in the crankcase as long as it's reasonably close to the spec (grade can vary a bit, etc). So the UOA is telling you that the combination of the lube, plus the design and manufacturing of the equipment, are working well together.
Conversely, there are engines that have much higher wear rates; the old 350 SBC will shed about 5-7ppm Fe every 1k miles, or more. it does not wear well at all, but that does not stop it from running well. And no matter what lube you use, it won't affect the wear rates that much.
Each engine family has a "normal" wear trend tendency, and each individual engine produced will have a unique response within that sense of "normal".
UOAs can certainly tell us about the performance of a lube, but that performance ("quality", if you will) is only a part of the overall interaction. You can make some generalization and be OK.