Originally Posted By: CATERHAM
I've used the Toyota 0W-20 and it shears about 10% (oil pressure drop) within the first 150 miles of being in service but then stabilizes.
Not to criticize. But a couple of things strike me as limitations of using oil pressure as a measure of oil viscosity.
1. It seems a bit of a crude measurement. ("Crude" as in "rough".)
2. It says more about kinematic viscosity than HT/HS. My understanding is that VII improvers do not manifest (as) much effect under high shear conditions. So if the lubricant package shears 10%, I'd expect a smaller effect on the HT/HS. Which, IMO, is a far more important number than the kinematic viscosities.
There is a very real problem, I think, in the fact that the information which gets published about oils is largely useless or misleading. From KV40 and KV100, we get a number called VI. But is it really useful? To the extent that interpolating between 40C (104F) and 100C (212F) is useful, we're on pretty solid ground.
Less so when we move from interpolation to extrapolation outside of the 40C-100C range. Which is what we almost always want to do.
HT/HS viscosity, at 150C for new oil is generally published. (Except that BP can't be bothered.) And that's nice. But almost no data is available about what happens after it is run a while.
For cold weather operation, some genius decided that what people really want to know is how thick a syrup their oil is at temperatures that almost nobody ever experiences. (-40C/-40F)And either the same, or some other genius decided it would be a great idea to test different oils at different, irrelevant temperatures. (-40, -35, -30...)
Come on. Most of us would like to know how the oil does at maybe -15C. Can we reliably extrapolate from the 40C-100C numbers all the way down to a frigid -15C? Well, trying to do so down to the published -30C to -40C numbers certainly doesn't get us anywhere. It doesn't work at all.
From the popularity of API viscosity classes (XwXX), all the way down to the most detailed numbers that get published, the system seems totally [censored]. And I see no indication that there is any effort at all to fix any of it.
Since real-live tribologists are, presumably, not stupid, I infer that industry insiders have access to much more useful information than the mostly useless statistics that we armchair folks generally get to see.
I vote we go get our pitchforks and storm the castle now. ;-)