I'm not going to go off again because I addressed the OPs specific point about "today's oils,,, older engines".
Yes, it is a fact. Yes, it can be proven. The whole change in modern oils began around 1995-6. That was when we first saw "for use in gasoline engines only". Before those days, oils were for gas and/or diesel engines. The change came about because a small change in engine oils for autos could reduce internal friction and also protect the cats that were required to lower tailpipe emissions.
Only regarding the ZDDP additives of the time, this is when 'modern' oils began to lose this cam anti-wear additive. SJ API class was limited to 1000ppm ZDDP, starting in 1996. Prior to that, most oils had around 1200ppm, and some were higher or lower depending on the other additive package from various vendors.
After SJ was SL with another reduction, but I don't recall or have the spec. Whatever it was, it was lower than 1000. SM is 600ppm, and SN becomes complicated because the ZDDP levels are constrained by weight classification. This sort of makes sense, because modern engines using a 0-30 or 5-40 will not tolerate much ZDDP, but an SN classification with a 20-40 or 20-50 may be used in a late 90s engine needing more ZDDP. I don't know the specs on those breakdowns by vis index.
High performance engines of the late 80s and early 90s are the most exposed to the 'older engine, newer oil' failure mode of cam wiping or lifter spalling. The changes in the spec were done for the value of making the fed mandated 100,000 mile warranty on emission components of the cars. Some folks don't even know that there is a 100k miles mfg warranty of ALL emission components.
I has a 1985 Nissan pickup with 88k miles on it when the cat failed. I took it right to Nissan and told them to repl my cat for free because it failed. We argued for a while, but eventually they had to do it, because of the warranty.
So, whether one wants or doesn't want the correct range of ZDDP additive, it's fine with me. I know what to do with those older engines, and I'm sure there are plenty of empirical cases where 'my 1959 Studebaker is running just fine with new oil!' and I don't discount that. I'm sure the Studebaker 6 engine cam to lifter pressures are the same as a 7200RPM Lamborghini engine with flat tappets, and dual valve springs. Yeah - sure....
This post was edited by docmirror on 03/14/2023 at 01:21 pm.
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