I only lightly skimmed the thread
But to be entirely honest I'm rather dissatisfied at both his testing methodology and conclusions. Though, as a disclaimer, I couldn't view the images he posted as I opted not to register an account for this one task. If he's posted any UOAs I'd like to review them.
1. He seems to be trying quite hard to correlate oil temp with effectiveness. I would argue it's more of a result of flow rate within the system rather than internal friction. After all, when an engine is running, everything operates on a hydrodynamic film. The parts don't actually touch eachother. It's possible he's measuring pumping losses but without any data on wear rates, those datapoints are meaningless.
2. OP ran out of the gate with a thinner oil than what the manufacturer suggested. Seems to contradict earlier points in this thread (the ones I challenged)
3. His comment/concern about oil frothing at the end of the thread is, I think, presumptuous. Again, too much time staring at numbers and trying to make conclusions rather than taking some measurements and observing results. Can't say oil is frothing based on a 3psi pressure delta. Would need a sight glass. Could potentially measure it, at least while flowing, with some sort of light diffusion test.
4. Oil film strength as a product as viscosity I think really undersells an interplay of multiple variables. We're not dealing with a static situation here. It's actively pumped and the oil film being replenished. Take it to the extreme of too thick and you won't have the flow rate to appropriately replenish the cushion of oil by the time the crank swings back around. you could also run into cavitation issues which would eat a bearing very quickly.
5. To be clear, my comment is on street vehicles. If you're racing, you should really know better than to run blind period. Everything will be determined per application. So don't go pulling up racing articles about oil viscosities showing wear rates. Those vehicles typically run a higher oil temp than you'd see during street use (duh) and actively need a thicker oil to compensate for temperature thinning. With that said, I maintain my point that MFRs aren't speccing thinner oil and seeing reduced engine life. I've yet to see any substantiating evidence that doing so reduces engine life. They're not going out and designing an engine then tossing whatever grade of oil in there is the thinnest they can get their hands on. Bearing tolerances, flow rate, bearing size (and by some extension bearing pressure/area) are all part of the design. If you do some poking on BITOG, a couple members have found benefit in running thinner oils in their engines, though once again, this is per application and the results determined through testing - it won't be indicative of every vehicle. Xw20 has been around now for over a decade. And while I hate to introduce personal experience as without documentation, it's more anecdotal than anything, I've seen dozens upon dozens of vehicles come in with 300k+ miles - taxi fleet stuff - that have been running the manufacturer recommended since day 1. Even had a couple 400k tahoes/yukons still ticking away on 5w30 - though one had some good rod knock. Always came in dipstick dry and overdue though, so no conclusion can be made here if an Xw40 would have been beneficial from a wear perspective (oil burning/leaking and owner negligence not withstanding)
So I suppose the debate still stands. Need concrete evidence that manufacturers are recommending thinner oil, which then results in a lower engine life.
Sorry OP for the thread hijack. If anyone's interested in continuing to discuss this, shoot me a note or we can make a new thread and continue jabbering there. I like our tech chats
![URL]](/proxy.php?image=http%3A%2F%2F%5BURL%3Dhttp%3A%2F%2Fs128.photobucket.com%2Fuser%2FBADGUYNY%2Fmedia%2F705740BE-4E33-4E7C-A7F3-AE083832509D.png.html%5D%5BIMG%5Dhttp%3A%2F%2Fi128.photobucket.com%2Falbums%2Fp195%2FBADGUYNY%2F705740BE-4E33-4E7C-A7F3-AE083832509D.png%5B%2FURL%5D&hash=248005b8261a8ebf3bf06c554f49adfc)
