Quote:
Originally Posted by Dezoris
I think Phil wont agree here. Since he is building race setups. But personally if you drive in real cold 6 months out of the year, real world sub zero starts and dont see track time during those months running a 40wt oil is just too much. Cold starts are bad enough but cold starts on thick oil just not worth the increased wear. Not only that its highly inefficient. For not performance applications for efficiency sake you want the lowest oil pressure possible trying to target that 10psi per 1000rpm. On a 40wt in winter you be running over 90psi at 2000rpm for a majority of the time until you hit 200F oil temps. Which wont happen with an air oil cooler.
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The number before the w indicates the lowest point that the oil can maintain a minimum pour point. The number after the w indicates the viscosity at a set higher temperature. A 0w40 will have a lower viscosity at cold temperatures and a 10w30. If you want an oil that gives relatively low viscosity when the engine is cold and relatively high viscosity when the engine is hot, a 0w40 should give you both of those.
The only caveat is that SAE allows oils that meet 0w30 standards to be labeled as 0w40 as well as oils that meet 0w40 standards.