Ok BINGO. I haven’t trudged through all of the documentation quoted here but if that truly IS what they are saying…now that is bad language, and not at all what is happening with these oils. It’s a “gimmick” in that what you are buying isn’t somehow “5” weight oil AND “30” weight oil, or just exclusively one or the other.
I dont have time tonight but I am going to read that entire long article. It looks very informative…and one section points exactly to this “language” issue as I’m referring it. I think you even said something to the effect. I am getting a bit confused myself.
I think the takeaway from all of this…consult your manufacturer. Or an engine builder with experience if you’re doing something radically custom. Because clearly, as stated, the “number” and I say that in quotes because it’s looking really aribtrary and meaningless at this point…the number you see on the bottle does not come from any actual metrology involved with the testing of oils. It’s marketing, and it’s supposed to eliminate the need to know any of this. As the writer says "if designing an engine was easy, we’d all be doing it.
Not that you should remain willfully ignorant, but to get the job done, just go by what the automaker says to use in it.:crackup
I do also see the writer’s point about working backwards from hot running engine —> cold dead engine, oil cooling down and thickening not heating up and thinning. Design and testing looks at the engine in it’s, well, useful and most heavily needed and used state to know what it requires for lubrication. And that’s at operating temperature, running, producing heat. Sure all that wear comes at startup, but far MORE wear would occur if things were not right for 90% of the time that the engine is running, which is under load driving around, at operating temperature, on a long hour or more trip at higher speeds. At least in this sprawled country, most people don’t make the proverbial short trip that is bad for your car because it leaves condensation around, etc…