Originally posted by geeeman:
[QB] Specific gravity refers to mass and density, usually in comparison to water.
-*-* okay, but does it in any way play a role in how much additives the oil will take or how clean it has the potential to clean or how hot or whatever... eeek, what if any does this play a role in oil performance?
Some of your additives are metallic soaps and likely raise the SPG. Esters usually have a higher SPG than the parafins. A higher SPG might indicate more of those components, but the manufacture's specs would be a much more reliable guide. Since the SPG range of different oils is fairly close and the oil is flowing under pressure, I don't think the SPG itself has much effect on oil performance. When comparing the SPG of 2 different oils, make sure both are specified at the same temperature.
Specific gravity varies with additive content and base oil.
In general synthetics are lighter. I have oils that range from .931 to .824
An 85w140 is heavier than a 80w90 with the same additive package.
An ISO 220 mineral gear oil will be around .88 while a synthetic one will be around .85
I don't think it has much to do with performance, but affects how many liters you get if they sell it by the kilo. (as does Chevron)