I'll chime in here with actual facts ...
- The Ford/Conoco SAE study (2007-01-4133) clearly showed that wear rates are higher at the front of every OCI. Undeniable in the results. They not only used UOA data, but backed that up with a completely separate methodology (IIRC it was component weight analysis), which showed the same wear rate conclusion; that shorter OCIs make for higher wear. Extending the OCIs out actually took the wear rates to their lowest levels.
Engine oils are subjected to a series of industry standard engine dynamometer tests to measure their wear protection capability, sludge and varnish formation tendencies, and fuel efficiency among several other performance attributes before they are approved for use in customer engines. However, thes
www.sae.org
- This UOA study covering (literally) thousands of UOAs shows the same conclusion; that shorter OCIs have slightly higher wear rates and longer OCIs see the wear rates drop (out to 15k miles, where my data stopped). This phenomenon was present in every engine series I looked at; 4.6L Ford, 6.6L Dmax, Toyotoa V-6, Detroit D60. This wasn't a few UOAs; this is thousands of UOAs studied with macro statustical analysis.
https://bobistheoilguy.com/used-oil-analysis-how-to-decide-what-is-normal/
It is completely accurate to say that significantly short OCIs do cause some manner of wear excalation, BUT, that should not be construed to mean it's overly detrimental. Changing oil every 3k miles isn't going to destroy your engine; not by a long shot. It's just that by doing so, you're cheating yourself out of the even lower wear rates of the longer OCIs, as well as the fiscal savings of fewer oil changes. It's not that anal retentive oil changes will kill the engine; it's that they simply don't improve anything, despite the theory to the contrary. There's ZERO PROOF that shorter OCIs reduce wear. There is PLENTY OF PROOF that shorter OCIs do elevate wear. I challenge anyone to show me that data which exhibits facts otherwise. Don't throw theory at me; SHOW ME THE DATA from a credible study.
However, there are things to understand and acknowledge in these general comments:
1) this does not address "new" engines; it's probably a good idea to do a couple "flush" OCIs on brand new equipment
2) this only addresses OCIs ranging from 3k to 15k miles; shorter and longer intervals past those limits were not studied
3) no oil can stop a design flaw in the equipment; it may or may not be able to delay the effects of a design flaw, depending on the severity and propensity of the flaw to reveal itself
4) the OPs question and the focus of the wear-studies was just that - to understand OCIs effect on wear. If someone wants to pay for UOAs studies on OCI effects on cleanliness, that'd be great !!! But let's stick to the topic at hand; OCIs and wear rates.
5) these studies are predicated on normal FF filtration and not use of BP, though data also shows that BP filtration has diminishing effect with shorter OCIs
6) these generalities are based on engine series, not individual engines. To know how your own engine responds, you need to confirm it with data
Side bar on the "yabut" denial of UOAs ...
It is 100% true to stay that UOAs are not a perfect tool, but they are BY FAR the cheapest and quickest means of estimating wear, and when used properly and with the understanding of their limitations, they do as good a job as any other means of estimating wear. They will never catch all means of failures; catastrophic engine failures may not exhibit the means for the UOA to detect it (UOAs need particles less than 5um in size, generally). But for every example of a failure they missed, there's probably 10 examples of impending failures they caught. Many SAE studies that use UOAs as a means of wear analysis also use a secondary independent means to also confirm wear. Whether it be component weight, electron bombardment, or something else, they typically don't rely soley on UOAs, but rather they use multiple methods to track wear metals. Every single means of measuring wear has it's pros and pitfals; not one method is perfect. When you can get two methods to comfirm the same resultant conclusion, that's as good as most any "expert" needs it to be.
If there are a few simple take aways from this topic, they would be these:
Shorter OCIs are not proven to reduce wear rates; though they are not "harmful" in a truly meaning manner.
Longer OCIs are indeed proven to reduce wear rates; obviously not the risk people perceive them to be.
If you're changing oil anywhere from 3k to 15k miles, it's "good enough" that the engine is not at risk. If you're chaning it towards the shorter end, and you feel good about that, well that's just fine. If you tend to the longer end, that's OK to. Anything in that range is going to be good enough for the engine.