75W-90 vs 75W-140

[Nicholas Cove]

Here is something to ponder. My manual states 75W-140 with friction modifier added due to LSD. I had the dealer do a Diff. fluid change before a cross country trip and stressed he use the 75W-140. After 300 miles into the trip I started experiencing what was obviously behavior caused by NO friction modifier being added. . Called dealer, they looked up service order and sure enough , no LSD additive used. In the conversation he stated that Diff. called for 75W-90. I had little lady get the manual out as we were driving and had dealer on the phone. Manual states 75W-140. OK, so I have to find a dealer to put the additive in. Dealer I find is very accommodating and takes me right in. He also states Diff. called for 75W-90. I show him my manual that says 75W-140. He checks with parts Dept. They say 75W-90. They let me call FCA customer assistance and they say 75W-90. But of course they are just some guy looking it up on the computer. Everyone agrees that the 75W-140 will do no harm, but I certainly do not need it with the service the truck see's.
Both dealers were using VIN to research proper fluid.

Note: My truck is 2017, 2WD with LSD 3.21 ratio
I have not had any problems since having the friction modifier added.

My manual calls for 75 90 as well.

 

[18GSMRam]

The problem with a printed manual or similar is it is uncontrolled at that point and it's out of date as soon as the manufacturer changes it and should be assumed it's out of date. I have seen several discrepancies between my printed manual and the online one from Mopar.

Always use caution when referencing printed documents in this day in age, I always try to find the electronic version from the manufacturer

 

[stuntcardriver]

I have a 2018 ram 1500 3.92 gears with lsd and the dealer looked up the gear oil by vin and told me 75w-90. I showed him the owners manual which state 75w-140. He said either is fine, but the 140 would be better if you tow a trailer. I went with the 75w-140. And yes you would need friction modifier with either oil.

 

[Wild one]

Seems like everytime they go after better milege numbers oils and fluids get lighter. I'm a little suspicious when the same diff from a year before specifies 75W-140,but the next year it calls for 75W-90 and nothings changed as far as clearances go.

 

[HEMIMANN]

I don't have gear tooth load profiles for these axles, but find it difficult to believe they need 140 wt gear oil except under heaviest tow loads in highest outdoor temperatures.

I'm talking about dump truck loads. Ford Super Duty also calls for 140 just to dummy proof them from early failure liability. I run 75W-90 synthetic in my heavy duty with AAM 11.5" ring gear. The manual properly says use 140 only for heavy loads. To me, that's over 10,000 pounds.

 

[Burla]

Gotcha, thanks all for the info. I dont do any heavy towing/hauling, or drag racing haha, so I’ll go with the 90 weight on my next fluid change, and make sure I get as much of the 140 out of there as physically possible

burla scratchy his head...

The lager and stronger the diffs like the 2500's you can use lighter oil, the reason they went to 140 weight in the 1500's is because they had issues. Mind you at a time where everything was going thinner, fca moved rear ends to 140w and had recalls as well.

 

[HEMIMANN]

burla scratchy his head...

The lager and stronger the diffs like the 2500's you can use lighter oil, the reason they went to 140 weight in the 1500's is because they had issues. Mind you at a time where everything was going thinner, fca moved rear ends to 140w and had recalls as well.

Yah, bigger diffs have more tooth contact area for bigger loads.

The same loading principle applies to smaller diffs - with lesser tooth area, heavier vis is needed at a lower high load, say app. 5,000 lb instead of 10,000.
clearer?

 

[Mister Luck]

Any oil thread has it’s truth’s and it’s fallacy’s or interpreted or misinterpreted information

What looks like the same differential across the board is not necessarily the same differentials internal components.

GL-5 is the common and requisite nomenclature for FCA Chrysler MOPAR differentials because many have specific metallurgical sensitivities to non GL-5 fluids.

Remember the engineers complied the data and it has been translated into a digestible form of context that has continuous updates and revisions.

The range of fluid weight specifications in the owner manuals are stated as “recommendations” with the exception of the GL-5 technology. It is not expected to negate common sense in application.