Front/Rear Differential Fluids

[corey148]

Good evening, looking for some clarification on the fluids needed. I currently own a 2018 Ram 1500 with the 3.92 rear end. I already changed the transfer case fluid at 30K and plan on changing it again since I'm at 60k. I will also be changing the front/rear differential fluids as well since they have never been changed yet. My question is the owner's manual calls for GL-5 Synthetic Lubricant 75W-85, however the cost of it is insane. Am I able to just use something like Mobile One 75w-90 Synthetic which is significantly cheaper instead. The rear differential calls for 75w-90 with approximately 5 oz of Limited Slip Additive, which is fine I will probably just use Mobile One again . Any clarification would be much appreciated!!!

 

[KKBB]

I would use what the manufacturer says to use, or an oil that meets specs. I say this because we have a 2020 ram 1500 limited and just did the rear diff...it called for 90w-175 strictly because of the limited slip 3.92 rear end. Maybe they changed what they recommended between those years, but I would verify just to be safe. Then again, being an 18 and 60k you probably don't have warranty, therefore use what you feel is best for your beast!!!

 

[Burla]

You only add limited slip if it is needed, literally all gear fluids except special order already have it in the formula, certainly all m1 will. You can absolutely use m1 and it is gl-5 which most likely anything you buy will be it is the only modern spec now for a lone time decades. All of those weights 85 90 or whatever winter rating you want 75 are all almost identical in every way, literally dumb to have these options, so yes you can use 75w80 that has been universal gear fluids for like 100 years, ok not that long but very long. Double check the rear number, most rams take 140w for the rear, and that you do not want to use 90 on. If something changes then ok, I will check that later. Look at Valvoline bags at Walmart, just as good no pump needed. If you get any shudder after you change the fluid, then you put small doses limited slip at a time til it goes away.

75w85 is visc 12 similar 5w30
75w90 is visc 16 similar 5w40

The only reason why ram asks for that in front diff is fuel mileage gov't CAFE numbers, visc 16 in gears is like 5w40, for me a minimum weight. The issue would be having thin fluid in there when they get hot, I'd stick with 90.

 

[corey148]

Thanks guys for the info. Much appreciated!

 

[Burla]

Thanks guys for the info. Much appreciated!

page 603 link below..

https://www.fcacanada.ca/owners/en/manuals/2018/2018E-RAM-15_25_35-OM-1st.pdf

You tell me, what's it say for rear diff fluid? Does your manual say something different...?

The 1500's NEED 75w140 for the rear, it is because they are weaker, the stronger 2500 models use 75w85 because they are stout and don't have the same weaknesses. A couple guys in the know says it is because of the clutching system in the 1500's, I do not know personally as I never seen one, but use the 140 weight there.

 

[Burla]

BTW, you have a nice truck there, the 3.92's with the 8 speed is kind of rare and cool in my opinion, you see a lot of 3.21 gearing, I'd take the 3,92's myself. How does that drive? Lots of low end power?