[patkeefe]

I think the variants in ingredients of gear oils have to do with the variety of dissimilar metals found in a gearbox, ie, hardened steel gears, brass synchronizers. Evidently SWEPCO was formulated by request of a Porsche race team.

That said, I did have to learn about this stuff once in engineering school, but thankfully, I've mostly forgotten it. I'm sure it is quantifiable. I do think it is a mistake to equate "thicker" to "more resistance", especially at room temperatures.

The old timers told me that during the second war, farmers used to put sawdust in the gearboxes and differential to quiet them down. Good gear oil must have been hard to obtain back then.

Also, you could also consult API and ASTM.