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<x-charset iso-8859-1>Hello- > > No, it means winter. It means the oil is "suitable for winter use." > > You're right, it stands for Winter. All it means is that the viscosity, when > measured at the "winter" temperature, which I THINK is 0C, fits in the > bracket which has been agreed to be labeled as a 10 (or actually 10W.) It's 40C. Yah, I know, thinking of a 40C winter day is silly :-). But, it's what the SAE engineers chose many decades ago when they were just barely beginning to figure this out and just about all oils acted the same (low tech). > The other number, the non-winter one, is a measure of the viscosity at a > higher temp, which I THINK is 100C. Correct - 100C. > It is perhaps interesting to know that the 2 viscosity scales are NOT the > same. In other words a 10W oil measured at the winter temp does NOT have > the same viscosity as a 10 oil measured at the "summer" temp. Exactly!!! So, when your engine is warm (like at 100C oil temp), it acts kinda-sorta like a 30, but when just starting to warm up (like at 40C oil temp), it acts kinda-sorta like a 10. Or, 50 and 20, or whatever your flavor of multi-vis happens to be. > BTW, I was VERY glad to read Shad's debunking of the "synthetic doesn't > remove heat well" myth. I don't have any way of knowing the truth on this, but > I just couldn't understand how that myth could possibly be true. Why thank ya :-). I *believe* (although am open to correction) that the myth began in the early days of synthetic oil formulation. There are three general classes of "synthetic" base oils: the first is esters (Group V), the second is polyalphaolefins (PAO, or Group IV), and the third is hydrocracked petroleum (a subset of Group III). Note that the last of these is only legally synthetic... in reality, only IV and V are real synthetic base stocks. Anyway, in the early days, oils were formulated with only Group V stock. This caused a variety of problems... mixing with conventional oils was an issue. High temp breakdown was an issue. And, from what I've gathered, heat transfer was an issue (not from the heads... we aren't oilcooled... but from the bearings). Nowadays, true synthetics use a blend of IV and V for their base stock. Take care, Shad Laws LN Engineering - Aircooled Precision Performance http://www.LNengineering.com ------------------------------------------------ To unsubscribe, E-mail to: <type3-off@vwtype3.org> For more help, see http://vwtype3.org/list/ </x-charset>