Here's an example where just a slight increase in UOA metals turned out to be complete disaster. The UOA didn't really raise any alarms that something major was going on - so more investigations were done. I've seen similar reports from people that had engine problems and their UOA wasn't some gigantic red flag, then they cut open the oil filter and tore down the engine and saw all kinds of major damage. AEHass - do you cut open and carefully inspect your oil filters?
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@TiGeo here on BITOG went through a similar thing with his VW and found the cam chain tensioner eating itself alive, even though the UOAs were not some gigantic red flag. Maybe he can post some links to this adventures on that. So there certainly are some major limitations to using UOAs to monitor wear.
Some sealants give false positives of silicates and elemental metals measurements with an ICP spectroscopy are limited to a certain range of particle size, usually four to seven microns. Generally, labs will tell you that parts per million (ppm) numbers in the one or two range can be nuisance...
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