Rubicon Diff Oil Consensus

[CRZYCDN]

So...if I read this right, all different take the same fluid? I wanted to confirm as I'm looking at doing mine this weekend. I have a 2024 JLUR-X auto.

As well my buddy has 2 4xE on Sahara and one Rubicon...

Will they all take the same fluid?

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[Deleted User 38384]

Do we have a consensus on Rubicon diff oil? I have read thru all the threads here, but I'm still confused. It seems Dana and Mopar advise different specs. Not sure who to believe!
So is it 75/90 front and 75/140 rear or do I just say screw it and use 75/140 all around?

Dana is the manufacturer of the differential, they have the lifetime of their product in mind when they are recommending what differential oil you use.

Mopar lists their differential oil based on a number of factors including mileage requirements by the government, EPA requirements by the government, and other factors which I can't think of at the moment.

If you care about the life of your vehicle and your differential, I would go with the Dana recommendation.

However if you would rather have better fuel mileage, and don't care about the lifetime expectancy of your differential, I would follow what Mopar says.

 

[Upnarms]

Better fuel mileage= less lifetime mileage imo. I have heard more people with engines, differentials, transfer cases crapping out at low miles in the past few years. The engines seem to have one thing in common.... they are spec'd for 0w 20. This thinner oil stuff in the name of fuel economy is taking its toll. Just my observation. My 3.6 had rockers go bad at 55k miles. A friend's 2023 Silverado threw a rod at 19k miles. I read all kinds of posts on this stuff across several manufacturers. I used to never hear about so many engine and component failures across the board in the past. Maybe it's just poor quality control and manufacturing these days. Maybe it's cause forums you hear more about it. I can't help but wonder though.

And to stick with the actual thread topic, 75 140 for both is what i run.

 

[CarbonSteel]

I use Valvoline 75w140 full synthetic in rear differential. This is on a 2021 wrangler unlimited rubicon with stock 33"tires. I checked rear differential temperature with a infrared thermometer at rear cover after a 20 minute trip on freeway in 98 degree weather and the hottest spot was 141 * at the upper portion of the diff. cover. Makes me wonder how hot they get on longer trips or with heavier 35, 37, 38 tires..

141°F is not hot at all since most axles run in the 180°F range. To answer your question of how hot they can get, here is my 2019 with 4.10 gearing and 33" tires running unloaded at 75MPH in 95°F weather:

 

[grimmjeeper]

Now it’s officially an oil thread

Wait. Needs one more thing.

Ok. Now it's officially an oil thread.

 

[JT1]

141°F is not hot at all since most axles run in the 180°F range. To answer your question of how hot they can get, here is my 2019 with 4.10 gearing and 33" tires running unloaded at 75MPH in 95°F weather:

good lord! 225* unloaded? Guess it's time I check mine.. Hope the 37's and 5.13s don't run that hot.

 

[CO2Wrangler]

Understand that the oil specification is for the “system” which has compromises for each component in the system. In this case the bearings and hypoid gears. What works for one component may not be the optimal for another.
I used to work for the company that supplies the tapered roller bearings for the JL differential, mainly the tapered bearings on the pinion shaft. I actually worked in the functional test lab and recall testing these bearings. Moving up to the heavier weight oil (140) caused the bearing test stand to run and operate at a higher temperature under the same conditions. This makes logical sense as the heavier weight oil caused more drag in the bearings. So in this case while a heavier weight oil is beneficial for protecting the hypoid gearset it might not be optimal for the bearings when in consideration of heat generation. If you are towing I would just put a good quality 75w/140 synthetic in and not think about it. The OEM spec 75w/85 also works well , again I recommend a good quality synthetic. The key is to use quality synthetics and change the oil as necessary to keep contaminates out (water, mud, dirt, etc) . Hypoid gear sets and tapered bearings in differentials have been around for going on a hundred years. My 52’ Willys with a Dana 44 runs just fine 50+ years later and they didn’t have the lubrication choices that are available today.

Look at this guy bringing science, engineering, and real experience to an oil thread! Get outta heeeeeere! /s

In seriousness, this is the answer I will use as my basis for diff oil changes moving forward. And thank you!

 

[Aussicon]

Almost sorry I started this thread now!
Screw it, I’m gonna drain the fluid and just pack the diffs with axle grease. Not from Valvoline, apparently they are now Arab owned. Maybe I’ll use Amsoil grease.
or something from Target or Starbucks or maybe just fill them with Bud Light. TGIF.
Seriously, thanks for the replies!!

 

[Pape]

Now that it become a oil thread I can post
In all seriousness:
Normal usage: 75/90
Heavy usage: 75/140

Change it regularly, do not wait for it to turn into grease

 

[GavinH]

Thoughts on Royal Purple?

 

[CarbonSteel]

good lord! 225* unloaded? Guess it's time I check mine.. Hope the 37's and 5.13s don't run that hot.

They do...an infrared reading is not as accurate as an immersed sensor (that I had on my Rubicon).

 

[mgroeger]

YOU MUST USE AMSOIL OR YOUR AXLES WILL EXPLODE. IT DOESN'T MATTER WHAT WEIGHT YOU USE AS LONG AS IT IS AMSOIL. AMSOIL 5w-20 GEAR OIL IS BETTER THAN ANYTHING MOPAR OR VALVOLINE HAVE. THERE IS NO BETTER OIL IN THE WORLD THAN AMSOIL. GOD HIMSELF MAKES AMSOIL.

 

[grimmjeeper]

Thoughts on Royal Purple?

Decent oil. Does the job just fine. Nothing special about it. It's a bit overpriced compared to other brands. If it was the only oil available and I needed some now I'd use it. But if there was a less expensive brand that meets spec I'd choose that.

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