Doug, you managed to discount my posting without responding to it in any meaningful way. I've noticed this to be your general debate style.
In fact, there is currently enough UOA data out in the public domain, on this and other boards, on the Mazdaspeed Turbo DI engine, to begin forming conclusions. You are correct that you cannot use UOAs across multiple engines of multiple types to gleen any useful data. However, it is quite easy with some bit of data processing to generate meaningful analysis results on multiple UOA data on engines of the same type. With the correct filtering and comparisons the information pops right out.
Doug, I don't expect you to trash your years of experience on the fleet you have analyzed. But that does not discount what many engineering and tribological studies have found, that UOAs can be and are used as a diagnostic tool for wear and failure prediction, and for oil performance comparison. Please hear me clearly. A UOA is a blunt instrument, since, as you rightly point out, there are multiple potential sources in an engine for any wear particulate. Nonetheless it is a highly accurate and repeatable instrument. As such, it can be used quite effectively for more than you choose to believe.
Because of the accuracy and repeatability of Rotrode and ICP Spectroscopy used in oil analysis, changes in the analysis record can be attributed to variables, and those variables can often be determined, assuming that you look at multiple particulate concentrations, across multiple UOA samples, of engines of the same type. Manufacturing variation in modern engine designs is exceedingly small. I can take advantage of this in analyzing sample data from multiple sources. I and others do.
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Wear metals are accumulative (they build up) during an OCI and it is common for some "old" lubricant to remain after an OC. Very few people will know how much is left in some engines especially where oil coolers and the likes are part of the engine's lubrication system
You point out something important. There is a widely held belief that the highest engine wear occurs right at an oil change. This is a misconception, because wear metal concentrations have been contaminated by left over oil from the change. Once this residual concentration is subtracted out of the analysis results, the early wear rate after oil change is close to the average wear rate. Most people do not take to time to determine this, but actually it's quite easy , using oil analysis, to determine what the residual oil volume is, and perform the proper corrections to the analysis record.
