can I use 75W-90 fluid in my rear differential?

[bwinterroth]

I have a 2000 XLS 4.0L V6 SOHC and Amsoil recommends 75W-90 in the rear differential, but the haynes manual says 75W-140. Can I use the 75W-90? Are there any negatives to it? Also will i need the limited slip additive as well? Thanks

 

[CDW6212R]

Use the friction modifier for all Ford LS differentials. Check the tag on the diff. cover. The ratio will be there, and an "L" will tell you that it has a traction lock. Example "3L73", or "4L10", or else "3 73" or "4 10"

The factory spec of 75-140 weight is to be able to never service it again. Use the synthetic 75-90's, and plan to change it every 50-100,000 miles. Good luck,
Don

 

[bwinterroth]

amsoil offers Dead Link Removed or Dead Link Removed Which one should i get?

 

[aldive]

I run Amsoil 75 w 90 in the rear of my /99 SOHC with LS. I have had no problems whatsoever. I do not use any friction modifier.

 

[Creager]

I do not use any friction modifier.

i was hoping someone would mention that.

Most Synthetics (personally I haven’t seen one that does not) already comes with a friction modifier already in the bunch. Adding more may lead to a consequential noisy rear-end and pre-mature wear of the differential.

If you use non-synthetic, chances are you will have to add Friction modifier.
Most shops should have it, and you should only put a 1oz for every quart. It might be 2oz though, my brain is going flat.

It should read on the back "CONTAINS FRICTION MODIFIER," or some say "FOR TOP-OFF ONLY” which in my mind says it already has some-kind friction modifier. But I could be wrong on that.

 

[CDW6212R]

amsoil offers Dead Link Removed or Dead Link Removed Which one should i get?

It looks like you should get the long life version, unless you will use the truck in very severe conditions(high heat of towing, etc.)
Don

 

[Creager]

Looks like Longlife 75w-90 with no friction modifier is what you need :navajo: