I have a 99 Limited that I need to change the rear differential fluid in. I had a recent engine oil change and I believe they (service station) removed the fill bolt on the rear diff to check the fluid level and didn't secure the fill bolt properly. I just happend to look under the vehicle a few weeks later and noticed a good bit of oil on the bottom of the rear diff. After checking I could turn the fill bolt by hand...I was fortunate that I didn't lose the bolt. I'm not sure how much leaked out so I figured now was a good time for a drain and fill. Here is my question...Is it safe to use 75w90 in the rear diff? I purchased three quarts of mobile 1 because the 80w90 or 90 wasn't available.

I purchased the 4runner with 106k and had all the fluids changed shortly after. I'm not sure what weight oil is in there now. Would it make more sense to shop around and find some dino in 80w90?

Thanks.

 

If you already have the oil I'd say use it. The difference between 75-90 and 80-90 is not very significant, I don't think you or the gears will notice one way or the other.

 

Go ahead and use it, won't hurt anything unless you are towing heavy loads or live in a very hot climate.

 

Someone please correct me if I am wrong, but wouldn't it seem like a 75w90 weight be a better overall choice over a straight 90w oil due to initial startup the oil should function like a 75W and then as it heats up it performs like a 90w?

 

I forgot our trucks call for 90, yeah then what the OP got is perfectly fine. Some of my cars call for 125.

The lower the W number the better.

 

i use 85w140 in my rear diff. i have an aussie, so i like it to be as smooth and quiet as possible. i tow alllllllll the time too.

 

It should be fine with winter coming up, as long as your not towing, it will be fine. I ran 75/90 in my truck many times because 80/90 wasn't in stock. I do recommend swaping all the fluid though, you will be surprised by how much crap comes out if it has never been done. It may be a waste of money to some people but I swap all my tranny diffs and trans case every 20-30k and I have a completely original drive train at 250k no problems and everything feels like new. Not so much of a waste of money if you never have to replace anything but fluids.