I don't believe this. I can see this is true with conventional oil vs synthetics, but not any full synthetic that meets SP and ILSAC 6. What is this mystery ingredient that cheaper oils do not contain?
There are tiers of formulation missing levels of quality between said tiers. It may not happen in all engines, but “passing minimums” often being the case with API ratings; doesn’t mean a perfect oil without limits as a result of “just meeting the minimums”…a lack of head room so to speak.
HPL called out OTS synthetics that simply could not clean or “run clean” as their oils are specifically formulated to do; but it comes at a cost. One doesn’t have to extend the OCI to benefit from “run clean” capabilities. Some engines are “harder on the oil” and will begin to have deposit precursors even during shorter OCIs. There is no one size fits all for every engine and use case.
However, this is where some lately have opted; for example an oil like VRP, to take out the guess work. VRP has a new additive that takes care of this real world problem occurring in engines using OTS synthetics. (Boutiques I also like for similar capabilities of “run clean” but also their capacity to extend intervals where VRP is questionable in comparison)
Sure, you could fault the problem prone engines and sometimes boutiques can still be pushed past their capacity, but it’s about repeatability and life of equipment implications. Had I known what I do now, I would’ve never extended my OCIs on cheaper OTS synthetics. Maybe M1 EP? Despite my little Honda Fit being easy on the oil, it has still experienced broken down oils leading to consumption issues all while producing superb UOAs on paper. The top end is spotless, but piston ring deposits and long term engine health begins to come into clear focus.
So, yes, in my case it was extending intervals on subpar lubes but the same happens in more demanding engines / use cases in shorter intervals. Lubes have limits and often it’s simply a price of formulation point.