Synthetic 75w90 - Rear Diff - Gas Mileage

[wallygetsit]

I just changed out the rear diff gear oil from the stock 75w140 to 75w90. We'll see if the gas mileage improves at all.

My expectation is it will indeed help, but how much... probably not much at all. 0.25 - 0.5MPG. Total guess.

I'll let you guys know.

Anyone else tested this change out... by itself? I see in the threads that many people have switched and all is well, but... any noticable benefits?

 

[Rage1973]

I have been looking into this also. I was thinking about changing to a synethetic gear oil. But from what I have been reading I need to get the oil that is for limited slip rear end. What brand of gear oil did you use??

Jeremy

 

[BrooklynBay]

I use Richmond Gear synthetic oil, which is the thicker one. I would say to just stick (no pun intended) with the heavier gear oil. It will stick to your gears more than the thinner oils that run off faster.

 

[wallygetsit]

I used Royal Purple 75w90 synthetic. If you go to their website, it talks about not needing a friction modifier additive, because how they blend oil.

I have a 97 Sport with the 4.10 limited slip rear end.

 

[aldive]

I have been looking into this also. I was thinking about changing to a synethetic gear oil. But from what I have been reading I need to get the oil that is for limited slip rear end. What brand of gear oil did you use??

Jeremy

Most synthetic gear oils have friction modifier in the mixture already.

I currently use Amsoil gear oil and prior to that used Mobil 1 and never added any friction modifier.

Good luck ........

 

[snocross1985]

I used Mobil 1 synthetic in my LS rear end with no friction modifier as well.

 

[celly]

I just put Amsoil Severe gear 75/140 and didn't use friction modifier either. 3.73 LS. No issues. I also don't see 75/90 saving much fuel. My Amsoil guy recommended 75/140 because of the additional stress the rear faces. Then again, it's Amsoil so using 75/90 wouldn't be a problem.

 

[ExplorerDMB]

I have Royal Purple synthetic throughout my drivetrain (except engs/trans - since my trans is already MercV which is semi-syn). I have noticed about a 1mpg change which is good enough for me. Runs at a cooler temperature probably too

-Drew

 

[aldive]

I use 75w90 Amsoil with nary a worry.

 

[snocross1985]

The Mobil 1 I used was 75w90 as well.