2017 Ram 1500 3.92 LSD Fluid

[Burla]

Late model Ford, GM and even Toyota half ton trucks all spec similar lower gear oil weight grades for their differentials. If RAM has been factory filling 1500's with these lower weight grade gear oils since 2017, one would think the internet would be littered with reports of catastrophic failed differentials if these lower weight grade gear oils were not doing the job.

In my opinion, I think sticking to a quality full synthetic gear lube is going to be more important than worry about perception of 90 vs. 140 weight grade gear lube.

Some paper out there was that ram was doing this heat transfer because 140w in the cold had some issues, so all we can do is speculate why they spec'd 140 weight in the first place. It makes a lot of sense, 140w in the cold and towing out of the gate sounds like it could be an issue. But it really comes to the reason for the heavy spec in the first place, which all I can do it guess. I think we did what we could on this subject a few years back, but I don't remember anything definitive. I think guys in cold places should consider this and talk to the local dealer. I think guys in warm places can get away with running 140w w/o issue.

 

[Tizzy]

So, was it ever decided what viscosity to use? I tow (heavy) in the summer and run empty all winter long (cold WI).
2017 1500 3.92 LSD

 

[18GSMRam]

Download the online manual (more up to date than printed material) from the mopar website to be sure, my 2018 1500 calls for the 90 weight and an additive for the LSD. Ram changed it at some point.

Anything printed should automatically be assumed to not be current as it's no longer a controlled document.

 

[bigred90gt]

I never doubted you and never called you anything, I simply posted your 2018 manual online. Don't blame me for what the 2018 online manual says, I didn't write it.

I saw the other manual posted as well that verified your position. Ram apparently changed the spec sometime in 2018 as 5 gens are calling for 90 weight as well. If it were me, I'd find out why they changed the spec, especially those with pre heated diffs. Now diffs run hotter, and they call for thinner oil, and fca thinks this was smart? I hoped they actually changed the diff to accept the thinner fluid.

Strange that they would have changed the online and hard copy owners manual in 2017 to 90 weight, then changed back to 140 in the 2018 online version, but kept the hard copy at 90. Someone must be drinking on the job again. Here is what my 2017 online owners manual says.

 

[grizzstang]

I run the 140 in the rear diff year round.

We get cold here but my truck really doesn't sit outside in the brutal cold anyway.

I want the protection in the summer when I am towing my travel trailer.

 

[18GSMRam]

Strange that they would have changed the online and hard copy owners manual in 2017 to 90 weight, then changed back to 140 in the 2018 online version, but kept the hard copy at 90. Someone must be drinking on the job again. Here is what my 2017 online owners manual says.

View attachment 244534

My 2018 online version I downloaded is the 90 while my hardcopy manual that came with the truck is for 140.

What's weird is the online "manual" that is dynamic, that is a viewer within the website, calls for 140.

Indeed someone has been drinking

 

[Oilman2383]

I am not sure what would lead them to make a change in oil weight like that, but one thing I would like to mention is both 75W-90 and 75W-140 start off cold as a 75W. It is only at operating temperature that there is a difference in weight, 90 vs 140. So cold temperature shouldn't be an issue. Must have something to do with gear set operation at temperature.

 

[Tizzy]

Well, my 17 lsd just got a shot of redline 75-140. I’ll try that.

I’ve got FM if I need to add any. 1-2 oz at a time, or throw the whole 4 oz in a once?

 

[Burla]

Well, my 17 lsd just got a shot of redline 75-140. I’ll try that.

I’ve got FM if I need to add any. 1-2 oz at a time, or throw the whole 4 oz in a once?

you wont need it, but if it shudders basically unheard of, then yes one ounce til it goes away.

 

[Daniel Ortiz]

Of course I just read through this thread after doing full fluid change on all my chassis stuff a few weeks ago. I went with 75W-90 in the rear based on a PDF copy of 2017 1500 manual I've been using. Looking at the printed copy in my glovebox, it says 75W140. Sheesh. I'm imagining a Flora-Merryweather style battle ("Make it blue! Make it pink!") between the gonzos deciding which weight to settle on. It looks like the 75W-90 guys ended up winning, but not before confusing a bunch of us 2017-2018 owners.