Well, BITOG hasn’t really come through with anything substantial, other than someone pointing out to me that Eni was Agip (which a quick Google would have told me) and saving me the face-loss of having it pointed out here.
“Thin-is-better” seems to be pretty much recieved opinion now, so the counter-assertions you’re getting here are fairly “old guard”.
Evidence-wise its mostly unsupported opinion or anecdotal either-way, though some peoples anecdotes are better than others.
An oft-cited presentation of the thin-is-better argument (mentioned in passing in the BITOG thread, though I’ve seen it before) is from Dr.A.E.Haas.
ferrarichat.com/forum/faq.ph … s_articles
He’s not a tribologist (but then neither am I) but a plastic surgeon (hence the surfeit of Ferrari’s, if you can have a surfeit of Ferrarri’s) and he’s based in Florida, so cold starts are’nt likely to be a problem for him. He’s a big fan of thin oil, and, while I’ve only scanned it, his arguments mostly seem to make sense, except his (fairly central) flow = lubrication assertion, which doesn’t. Provided a bearing is oil-filled, the dynamic component of hydrodynamic lubrication will be mostly contributed by the rotation of the shaft. I doubt pumped flow is much of a contributor. It’ll help remove heat and debris, but that isn’t lubrication as such.
Shiadoa’s report of “Cosworth engines, rattling badly ( hydraulic Tappets) on tickover.” is an interesting counter-anecdote.
I’d speculate that, if this was on (or shortly after) startup (the situation where 0W oil is supposed to be superior) then it suggests that the 0W oil doesn’t provide sufficient “cushion” for the (sliding?) cams and/or it isn’t reaching the top end to pump-up the tappets, perhaps because the thin oil is leaking back too fast through other bearings, or perhaps through the oil pump itself. This would perhaps be more likely with older, worn/wider tolerance engines.
If this was after the oil has reached operating temperature, then it’d suggest that an oil which has all its viscosity contributed by viscosity index improvers doesn’t provide sufficient “cushion” for the (sliding?) cams.
I dunno, (though I tend to be reactionary about this kind of thing) and if anyone else does, AFAIK they’re keeping quiet about it. Car companies are tending to specify thinner oil, but they have mandatory fleet fuel consumption targets to meet which are intended to carry more weight with them (and with many owners, of course) than prolonging engine life.
Though it doesn’t much help, I can’t help feeling that the specification of OW oil to reduce startup wear is something of a red herring. If car companies cared about startup wear, they’d fit a 50$ prelube system (a one-off capital cost) and we could use straight grade oil.