Doug may have proven something wrt large diesels with extravangant oil capacities in hard service.
This has negligible relevance to the vehicles that most of us drive, so it proves almost nothing.
I am quite sure he would beg to differ on that one.
What Doug did show, and or very own Dave Newton has shown the same, is that condemnation limits for oil in service can be far beyond what most of us would feel comfortable with
Agreed. And that ties into the value aspect of things. If you aren't going to take advantage of the potential service life of the lubricant, what is the point in tracking it? Assuming an engine in proper mechanical condition.
Of course the notion of a teardown and measurement is silly.
You're not going to do one and I'm not either.
They are far from silly and I've done several. I've posted pictures of them on here in fact. As well as the tear down and build-ups of a number of 302's.
UOAs are a valid proxy for wear.
In your opinion. This is where we disagree.
To postulate that the metals could be coming from some source other than wear is reaching, and an owner normally knows when rust would be contributing to high iron levels, as in cases where the engine has been left resting for a few years and is then put back into service.
We are talking about parts per MILLION and particles that are 2-10 microns in size! It doesn't take much rust to affect the readings. In fact it doesn't take much of anything. Did you see the UOA from my Town Car when the engine was opened and the heads swapped? We are talking iron in the over 100ppm range on what was fresh oil.
Your other two examples are specious, particulary in the context of the many UOAs you can find here of most common engines, and I doubt that you'd need thousands of them.
Doug seems to disagree.
If your street driven engine has metals per K well beyond the norm as compared to other similar engines, then you may well have a problem. It may involve the oil you've used, it may involve the drain intervals you've used or it may involve your driving habits, but one could draw a valid inference that something is amiss.
Certainly. but that's not the same as seeing +/- 10ppm between oils and drawing the conclusion that there is a (significant) difference in wear between the two lubes. Using the tool to detect a problem is part of its purpose. Those are not the same thing!
Manufacturer's base their oil and OCI recommendations on an expected vehicle service life of around 150K and this is well understood in the industry. Many may not find this to be an acceptable life and will therefore maintain their vehicles more carefully than what the manufacturer calls for. This may include periodic UOAs just to see what's going on and to try to achieve lower wear. Acceptable to me might well be a lower number than acceptable to the OEM, since the OEM has designed both the vehicle and the maintenance schedule around what many of us would consider to be too short a life in service.
Yet many engines in certain families with regular maintenance go far, FAR beyond that with no special maintenance regimen and no special lubricant that is based on a myriad of UOA's performed to "optimize wear". And of course that ties into your next point:
The longest lasting engines typically get that way because they have low specific outputs or they're operated in a way that only produces low specific output, like mainly highway use. Any engine can be made to last a long time with careful maintenance as well as careful driving.
While that is generally true there are many engine families that simply don't last due to mechanical defects that manifest themselves later in life. And some engines (like a few Honda and BMW ones) will rack up plenty of miles even though they have relatively high power density. With the Honda example, they will do it on whatever PCMO in the right grade is on sale.
Any engine can be ruined through a lack of maintenance just as it can be through abuse.
Certainly, but we are talking about optimizing engine life are we not? Yet some engines have proven that they'll last and last and last without any optimization. Their design is conducive to a very long life. All engines are not created equally.
There is a very fine line between maxmizing oil life and going beyond an oil's life limit in service. Where that line lies is a matter of opinion. I know that Dave Newton and Doug Hillary would put the condemnation limit well past what the UOA lab I use, Polaris, does. Polaris also flags TBN levels that Blackstone recommends as good for continued service.
I suspect that Polaris may know a thing or two about oil service life having done who knows how many UOAs over the years and trended many engines in commercial service.
But have they done tear-downs? That ties into my earlier point in that determining lubricant life in service part of Doug's protocol was also to perform random tear-downs to actually LOOK at the components. He wasn't drawing his conclusions based on the numbers on paper, he was drawing them based on actual measurements and physical inspection of components. That's one of the bigger gripes I had with Dave's testing, that he didn't do that part of it, he looked at lubricant health as his metric and that was it.
Of course, if you reject UOAs as having no value, then that means little.
Luckily none of us here are doing that

We are just debating their applicability to measuring wear. I think we all acknowledge their significant value in determining oil life, contamination levels and alerting us to potential issues with a piece of a equipment.