QUOTE (3YLSYKR @ Apr 17 2012, 04:47 PM) <{POST_SNAPBACK}>
I have used Royal Purple 85-90 and seems to work well.
Do you mean MaxGear 85W90? That is an API GL-4 GL-5 gear oil, particularly for hypoid gears. While it may work, the manual specifically says not to use hypoid gear oil.
I was confused by the manual stating to use an 80W or 85W in the transmission. Wanting to use RP I fired off an email to them and here is some info I got back from Royal Purple when I addressed this question back in 07:
"If the OEM is listing an oil by SAE Gear oil viscosity grades such as an 80W or 85W but also specifying NOT to use a hypoid oil (also considered a API GL5 rated oil for hypoid gears in a rear differential) they are telling us to use basically a motor oil, atf, or industrial type turbine quality oil in the appropriate viscosity grade.
This might be attempt by the OEM to push retail consumers back to the OEM Service Department to sell a branded oil as single grade SAE 80W or 85W non hypoid oils are NOT common in retail outlets.
On the attached Viscosity Comparison chart - you can see that an SAE 80W = an SAE 20W crankcase oil in viscosity.
An SAE 85W would be that of an SAE 30W.
This would be the RP Synchromax - which has a viscosity of 7 cSt @ 100 C or a light SAE 15-20W.
For racing, you could also use our XPR 5W20 or XPR 5W30 oils.
For routine use - an alternative would be our RP 10W30."
David Canitz
Tech Services Manager
Royal Purple Ltd