Originally Posted By: Mr_Incredible
Certainly the usual UOA isn't up to accuracy standards of, say, any nuclear research lab. But they'll do for $25. It's at least better than killing a chicken over the used oil and throwing the bones.
But also, your point is pretty much my point. Switching to 20wt isn't an instant death sentence for your engine. The difference on mine was not significant. Some engines may be prima donnas, but that one certainly isn't. No true difference on an already-279k mile engine.
What I was trying to say is that the minute variances in PPM between the two is not enough to draw any sort of conclusion from. Inexpensive UOA's are a great tool for monitoring contamination, oil life, and to check for things like coolant leaks, air intake tract leaks and the like. But they are not meant to contrast one oil brand to another or one oil weight to another.
UOA's are not to be relied on to tell you how your engine is "wearing". They can show you if there is a problem (large spike in a particular wear metal like lead or copper for example can indicate a bearing issue) but due to the rather narrow range of the sample particle size, they are not a "wear" determination tool.
Think of it this way:
Oil A allows an engine to shed 5ppm of FE at 2-microns and 50ppm of FE at 8-microns over 5000 miles.
Oil B allows the same engine to shed 9ppm of FE at 2-microns and 1ppm of FE at 8-microns over 5000 miles.
In a UOA, the FE in sample A would show lower than sample B, because the UOA doesn't detect the larger 8-micron particles. So people would then argue that oil "A" is providing better protection and lower wear than oil "B" based on this. Yet in reality, oil "B" is protecting the engine better, since it is shedding fewer large iron particles.
I probably sound like a broken record, but Doug Hillary wrote up a very nice article as to the accuracy and value of inexpensive UOA's. If you haven't read it (which from your posts, it sounds like this is the case) then I highly recommend it:
http://www.bobistheoilguy.com/used-oil-analysis/