Posted by Ben on November 17, 19100 at 20:53:13:
In Reply to: Gear Oil Question posted by Herman on November 17, 19100 at 09:47:46:
IMHO, any oil will do for normal duty and if it's changed by the book, BUT, if severe duty is the case, then you'll need better oil (better is my opinion).
First this tidbit, the gears are not supposed to actually touch each other. There should be an oil film on each tooth's surface that actually transmitts the force. Not an issue with high speed gear boxes, but on low speed gear boxes (our differentials are this below a certain speed depending on ratio) the gear faces stay together longer. Force also plays as it is what squeezes the oil film off. Shock is a ditto.
The ability of the oil to film on the surface and stay there is determinded by the tensile strength number. The higher, the higher the ability to stay. Heat, water (impurities), time affects this number.
Foaming is an issue because 1) it can not disapate heat well, 2) the bubbles on the gear teeth surface "pop" and metal to metal contact is made.
So, that is why there is an "extreme pressure" (EP) additive for heavy duty usage. That increase the film strength (tensile strength number) and anti-foaming additative.
Dino oils ahve a lower temp tolerance, have lower tensil strength number and don't last as long as synthetics.
I'd not buy any of these things from a dealer, as their mark up is too high, and the only reason I buy from a dealer is if it's not available elsewhere. I would buy Mobil 1 synthetic gear oil and it sounds like it would be less than the dino oil from your dealer.