Amsoil gear oil...

[35Remmy]

Conventonal 75w90 Valvoline dura-blend gear oil after 1 hour drive at 70 MPH. Rear pumpkin WARM to the touch. Amsoil same weight after same drive BARELY warm. Can hardly even tell. I am sold.

 

[Mike Tonon]

Originally had 80w90 in my rear diff, put 75w140 in, thinking it was the right stuff. I haven't looked much into it, but I haven't noticed a difference yet.

 

[85_Ranger4x4]

If it isn't transferring heat to the case where is said heat going? Is the oil also not get up to temp for it to transfer from being 75wt to 90wt? Parts like bearings are made to run at a certain temperature due to thermal expansion. Like the guys that put 160* thermostats in their engines thinking "cooler is better". No, it was designed to run at a certain temperature.

My '96 Explorer 8.8 (like most many mid 90's and later axles) is speced for 75-140. It has Mobil 1 in it now, unlike the vast majority of '96 Explorer axles running around without issue still churning whatever Ford dumped in them at the factory. I didn't want store brand and it came out about the same with normal name brand when buying the LS additive separately (it has it mixed in already)

Those clowns almost toasted a brand new 5.4 at the local dealer, the guy was on the program to send in an oil sample and they would tell him if he needed to change his oil or just his filter. Around 30k miles (the truck had the same oil in it since the guy got it home) the thing was so full of sludge the cam phasers couldn't work, it knocked and hammered like they do with bad phasers. They flushed and flushed and changed the oil several times and it came around and ran pretty good, didn't need any parts aside from gaskets. The guy freaked when they told it him they put Motorcraft oil in and he needed to change it more often. He couldn't wait to get home and put more Amsoil back in it. They must have some pretty good cool-aid

 

[Mike Tonon]

My '96 Explorer 8.8 (like most many mid 90's and later axles) is speced for 75-140.

My owners and repair manuals say 80w90 for a 2007 Ranger 8.8 except for the FX4 8.8 (I think it has more splines, 31 instead of 28. I think that's the only difference.) the manuals call for 75w140. Should I change back to 80w90?

 

[35Remmy]

85 are you saying Amsoil had him on a program to run an oil analysis?

I would think if the pumpkin is significantly cooler the lubricant is doing a better job than what was in there, I.e. reducing friction. Just my 2 cents.

 

[4x4junkie]

I would think if the pumpkin is significantly cooler the lubricant is doing a better job than what was in there, I.e. reducing friction. Just my 2 cents.

I would agree.
A differential (and also a transmission) is very different from an engine. Any heat generated within it comes purely from friction (between it's moving parts, as well as from how easily (or not) the oil can flow within it). Any reduction in heat generated should appear as a gain in MPG (though it's not likely to be very significant, if it's even noticeable).

My owners and repair manuals say 80w90 for a 2007 Ranger 8.8 except for the FX4 8.8 (I think it has more splines, 31 instead of 28. I think that's the only difference.) the manuals call for 75w140. Should I change back to 80w90?

Probably couldn't hurt to change back if it's cold where you are (the thicker oil might be dinging your MPG slightly). It's not going to hurt the axle itself at all though.