Originally Posted By: PeterPolyol
GLG1 and kschachn aboth have points IMO. It seems obvious that the W rating system was indeed borne out of a need for easier (or just plain possible) unaided starts in winter. It's obviously a rating system we need to determine the multigrade performance of an oil in the cold, since the KV100 viscosity does not correlate at all.
That said, it's been a while since the standard's introduction and priorities have radically changed. Regulatory bodies have, and still are, driving engineers to desperation to milk every last drop of friction out of the assembly during testing. The resulting low viscosity oils are pushing the SAE J300 to the limits- 15 years ago, we might have thought future grades would have followed 20 with 10, then 5 similar to the W ratings. Nope! They're splitting the remaining "20 points" 3 or 4 times just to keep the rating system relevant. The cold rating is already maxed out @ 0W with no indications of further definition. Pretty safe to say that attempts to achieve the lowest possible warm-up viscosity to reflect on regulatory testing results in oils that just
incidentally qualify for the 'bottomless' 0W rating, rather than being specifically formulated to be a winter oil.
Have asked the oil formulators on the board whether in their opinion, and I'll use things like M1 "Race" 0W50 "accidentally" meet 0W, or whether 0W is there by intent...the consensus seems to be that the 0W is a target, and met intentionally.
Just for S&G, here's some of the things I've collected over the years...
1923, looking at the SUS, you can see where the "grades" that we know came from...note the 020, and 030 for the cold temperature oils.
1950...things changed, to a proper W rating and an operating rating...based on viscosity at 0F
1967, again different, still 0F
Couple from my paper collection...1984, different W grades based on stable pour point temperatures, and when they were lost, borderline pumping.
Note the changes in metrics, viscosities, and the like that "defime the grades"...they are arbitrary, and reflect the learnings at the time, that 0F viscosity didn't tell you squat about -30, and later, neither did pour point.
A current 0W is clearly a -40C oil, while an 80s oil may or may not have been.
Thus I agree with the formulators that the "0w" is by design rather than accident. In the older versions of J300, they most certainly could have been an accidental byproduct of basestock.
I'll add this one too...this was Selby's proposed
And at some stage when they were fapping around, CAT split ranks with their oils...note that their view of HTHS rises with grade compared to engine oil J300 specs...(the way that it should be....M1 0W50 race oil should NOT be allowed to be called a 50 with an HTHS of 3.8).