Thanks for that thorough response (Post #9 in this thread). It suggests to me that oils meeting minimum standards may not be adequate for longer OCIs or more extreme conditions. Of course, this has been said here many times and the admonishment is often found in owners' manuals and service recommendations.
Yes, and as has also been covered, certain engines, the recommendations in the owner's manuals have proven to be wholly insufficient, like with the Honda VCM V6's for example.
It's often suggested here to buy the cheapest oil that meets the spec, and that may be acceptable advice for certain situations and engines, but in many situations, it may be advisable to run a better quality oil to assure long-term engine health and reliability. I subscribe to using a better quality oil just to be on the safe side even though, more than once, it's been suggested that I'm wasting money/resources by using M1 EP.
Yup, exactly. You saw that Toyota Matrix/Pontiac Vibe posted that was run on Quick Lube oil. It has extensive varnish inside, but still runs fine. For some people, that would be just fine, for others, not so much. That was using an oil that "meets the spec" at a conservative interval.
However, there's another aspect to this that gives me pause for thought. Blackstone (and other sources, such as found in
@dnewton3's article about engine wear suggests that there are no significant wear differences between oils and even the length of an OCI doesn't always affect wear. I think it's this article:
Reviewing UOA Data Used oil analyses (UOAs) are tools. And like most tools, they can either be properly used or misused, depending upon the application, the user, the surrounding conditions, etc.= There are already many good articles and publications in existence that tell us how to interpret...
bobistheoilguy.com
The article also indicates changing oil too soon can adversely affect wear, and that wear is reduced when the oil in the sump ages a bit. Might that be a good case to leave some residual oil in the engine when doing an oil change, such as changing the filter every other interval? Of course, even when changing out the filter, there's always some used oil left in the engine. The Camry has about 1.4 quarts that remain in the engine, others less.
Yes, but wear and cleanliness are not "joined at the hip". Also, it depends on how you measure wear. Are we talking about tear-down analysis, with measurements, or are we talking about PPM observed via UOA's? A lubricant that's saturated also won't hold any more metals in suspension, so those metals plate-out as part of the agglomeration and lay-down process, ergo, they don't show in UOA's. However, even if the wear rate is unaffected, varnish build-up can negatively impact performance in multiple key areas such as oil control, compression and VCT operation.
That said, the argument about tribofilms is sound. An oil that's still serviceable (able to continue doing all of its jobs) does demonstrate the best amount of wear control; lowest wear rate, in studies that specifically measure that. So, the key is to strike that balance and extract the maximum value from that lubricant, without taking it too far and risking varnish/sludge. UOA's that measure oxidation can help here, as do TBN/TAN, coupled with visual inspection.
What I'm trying to do is learn what may be the best balance between use and changes. Any thoughts you have would be welcome.
And I'd like to suggest to others here to read at least some of the articles found on this site's home page.
Optimizing OCI length with a quality lubricant so that the maximum value is extracted from that lubricant is one of the proper uses of UOA's. As was shown with Doug Hillary's testing, massive sumps filled with a high quality synthetic (Delvac 1 5w-40) with centrifuges used to keep soot out of the oil, could safely have their interval extended to around 60,000 miles, confirmed through tear-down testing, which showed extremely low wear (every "as new" at 1.2 million km) and also, no deposits, which shows the additive package was able to deal with the contaminants.