I wrote:
> > The SAE ratings for engine and gear oils are not directly comparable.
> Just wanted to reaffirm that this is indeed the case. From an essay on
> lubricants from Redline, I found the following:
> Gear oil viscosity is measured at 150 F vs. 210 F for motor oil.
> Therefore, 40 W motor oil is the same as 95 W gear oil.
Just realized that the second sentence could be taken out of context.
40W motor oil is only the same as 95W gear oil with respect to their
viscosity. The additive packages would be very different, however.
Other differences noted in the same Redline article:
Gear oil is acidic, motor oil is alkiline. Gear oil needs very high
wear protection - Extreme Pressure (marked as EP). Therefore, it has a
very high sulfer and phospor content. Sulfur and Phosphate reactions
start at a lower temperature, and Gear Oil has much more additive than
motor oil. This additive is corrosive to copper bearings and bronze
synchro rings.
Gear oils decompose at lower temperature, usually 250 F.
Hypoid type gear sets have a sliding rather than rolling action, and
therefore require much greater wear protection.
Gear mesh in Gears literally chops up and cuts apart the long polymer
chains of Viscosity Index improvers.
--ken
|