Rear Axle oil

[wrigley]

The owners manual calls for 75W-90. I do not have the limited-slip rear axle. Is it beneficial when changing the oil to go to a slightly thicker oil (75W-110) or just stick with the 75W-90. I do not tow at all or haul anything very heavy. Thanks
Mike

 

[Fast69Mopar]

The owners manual calls for 75W-90. I do not have the limited-slip rear axle. Is it beneficial when changing the oil to go to a slightly thicker oil (75W-110) or just stick with the 75W-90. I do not tow at all or haul anything very heavy. Thanks
Mike

Stick with the 75W/90 as the rear axle is designed to be run with that viscosity. Adding a thicker weight oil increases drag and rolling resistance in the gears.

 

[wrigley]

Stick with the 75W/90 as the rear axle is designed to be run with that viscosity. Adding a thicker weight oil increases drag and rolling resistance in the gears.

Thanks for the reply.
Mike

 

[Wild one]

I don't agree with 69,the diffs used to call for 75W-140 they dropped the viscosity for emissions and milege numbers,not to promote longevity of the rear end. A 75W-140 acts like a 75W-90 when the diffs cold,but gets thicker the hotter the diff gets,which is when you need the better cling and cushion effect the 140 provides.

 

[Burla]

40 weight oil such as used in hemi engines can go as high as 16.3 viscosity and still be a 40 weight oil, a thick 75w90 such as redline is 16.1 viscosity, your 75w140 will have a viscosity near 27. So they are saying basically use a 40 weight oil in the diff. Now, the 1500 diff is not like the 2500 diff, the 2500 is so stout it can use the thinner oil and not risk damage from heat buildup, thus the 2500 has always called for the thinner gear fluids then the 1500. Now, I do not know what if anything has changed from the 23 RAM to other 4 gens, but 4 gens have taken 140w forever and that was spec'd on purpose because there were issues with lighter oil in 3ed gen. Look it up, 3rd gen had 75w90 and some diff issues led 4 gen to use 75w140, and I guess now they went back to 3rd gen 75w90.

140w sounds thick, but when it is warm it isn't thick, if it were me I would use 75w140 in the 1500 diff unless I was in snow area and had audible issues with it when cold. Fast 69 is correct that does add drag, which is fluid between metal parts. Same thing when an engine rattles on 0w20 and goes smooth with 5w30, same exact thing the 5w30 that is smooth is a form of drag.

5w-30 vs 5w-40 (Part 1 Cruise)

Showing oil pressure difference between 5w-30 and 5w-40 motor oil when cruising at 70mph. Tested on a 2002 Pontiac Trans Am.Update April 2025: It seems this ...

www.youtube.com

 

[EdGs]

Aren't the rear diffs supposed to use 75W-140?

Did they change something in the 5th gens?

 

[RSZ2001]

Aren't the rear diffs supposed to use 75W-140?

Did they change something in the 5th gens?

2017 Ram decided 75W-90 was good enough.

 

[Wild one]

2017 Ram decided 75W-90 was good enough.

That's the same year they removed the 5W-30 from the engines. They used to have this note in the big 700 page owners manuals and the online manual up till 2017.

 

[Dan Topp]

Aren't the rear diffs supposed to use 75W-140?

Did they change something in the 5th gens?

Claim the posi additive is in amsoil already I use it anyway

 

[WY-Dave]

Rear axle lube weight (viscosity) refers to its thickness and resistance to flow, with common types being 75W-90 (standard) and 75W-140 (heavy-duty/towing). The "75W" indicates cold-weather flow, while the second number represents thickness at operating temperatures.

 

[wrigley]

Aren't the rear diffs supposed to use 75W-140?

Did they change something in the 5th gens?

 

[Wild one]

That was done for emissions and milege purposes,not for the life expectancy of the diff. Even if you have the locker diff,the clearances are all still the same as when they called for 75W-140 in the diffs. I'd rather give up that 0.001 mpg gain for longer life out of the diff.

 

[Burla]

That was done for emissions and milege purposes,not for the life expectancy of the diff. Even if you have the locker diff,the clearances are all still the same as when they called for 75W-140 in the diffs. I'd rather give up that 0.001 mpg gain for longer life out of the diff.

x2 good luck with it.