my owners manual calls for 75w/90 gear oil for the front and rear diff. is there any reason that you cannot use 80w 90 gear oil insted. the reason i ask is 80w 90 is plentiful. i can get it in gallon jugs, quart bottles whatever. 75w 90 only comes in quart bottle here and finding 5 in one store is almost impossible. just wondering what you guys think.

The way I see it, the thinner oil is needed when cold so that the oil can get everywhere. When it is thicker, it might not get everywhere as well so you will have more wear on things until the oil gets warmed up.

I been using 80w-90 for years no problem... Here is a video a shot a while back and found on the harddrive...

The way I see it, the thinner oil is needed when cold so that the oil can get everywhere. When it is thicker, it might not get everywhere as well so you will have more wear on things until the oil gets warmed up.

i can understand that it just seems to be such asmal differance in viscosity

I been using 80w-90 for years no problem... Here is a video a shot a while back and found on the harddrive...

http-~~-//www.youtube.com/watch?v=-HvtS74RG8w

appreciate that info. nice video. how knots on the forehead until you got used to working aroung that pair hanging on the receiver?

Those were a gift from a friend... http://www.trucknutz.com/

I know it's insignificant, but you wanted to know why and that's my guess.

I know it's insignificant, but you wanted to know why and that's my guess.

and i appreciate the opinion. sometimes insignificant things can lead very significant problems.

do i need any kind of additive in my gear oil when i change it and if so how much i have a 11.5 rear end. the dodge dealership said i needed it and its 12$ a bottle and i need two. i know how dealerships are so this is why im asking

If you have a limited slip axle yes you require it....Or you could buy the gear lube with the friction modifier already mixed into it.