Differential oil change

word302

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All owners manuals for 18 to 21 models say 75w85 regardless of towing and every tech at my CDJR dealership I work at says to use the 75w85 except for the M200 which is the Dana 35 I believe. No, the 75w140 probably won't hurt anything. I drove mine 16 hours to Moab wheeled for 3 days plus had the Jeep loaded down in the back. I checked the rear diff, and did not feel anymore warm than doing a 20 mile drive to town.
Yet Dana and the Jeep factory service manual recommend 75w140. I wouldn't put any stock in what a dealer tech has to say about anything.
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jellis4148

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The factory service manual doesn't recommend 75w140. Page 15 a guy posted off the Stellantis service page. Only for the M200 does it say 75w140. I'm sorry, I guess all dealer techs are idiots. Only people that work at other garages or shade tree mechanics know what you're supposed to do. Hell, why don't we all run 10w30 in the engines like we used to instead of the 0w20 it recommends. I'm sure somewhere on the internet someone says they still use 10w30.
 

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The factory service manual doesn't recommend 75w140. Page 15 a guy posted off the Stellantis service page. Only for the M200 does it say 75w140. I'm sorry, I guess all dealer techs are idiots. Only people that work at other garages or shade tree mechanics know what you're supposed to do. Hell, why don't we all run 10w30 in the engines like we used to instead of the 0w20 it recommends. I'm sure somewhere on the internet someone says they still use 10w30.
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Yes, most all that work at stealership Service Departments are idiots... Yes they are...

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jellis4148

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@jellis4148

Yes, most all that work at stealership Service Departments are idiots... Yes they are...
And I suppose you are the greatest most knowledgeable mechanic the world has ever seen. People come to you from all over the world just to have you fix their car.
 

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jellis4148

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Knock on wood. I have 30k on my Rubicon. I change the rear every 15k, and the front every 30k putting the 75w85 in. We go wheeling about once to twice a month and have 0 issues with the lockers. I agree potting probably helps, but from what I can tell the biggest problem is the metal getting in the PCB causing the problem. That's why changing the fluid so often is recommended. I know it's not a complete open and shut case, but most people I have talked to with that problem either didn't service it enough or at all.
 

word302

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Knock on wood. I have 30k on my Rubicon. I change the rear every 15k, and the front every 30k putting the 75w85 in. We go wheeling about once to twice a month and have 0 issues with the lockers. I agree potting probably helps, but from what I can tell the biggest problem is the metal getting in the PCB causing the problem. That's why changing the fluid so often is recommended. I know it's not a complete open and shut case, but most people I have talked to with that problem either didn't service it enough or at all.
You are completely incorrect. There is great advice in this thread and you’re just spouting your own opinion as fact. People have lost locker sensors in as little as 1000 miles. It doesn’t matter how often you change your fluid, once that seal breaks your sensor will be toast soon. Also do you think Dana knows anything about these axles? If you don’t like what’s being said here just move along.
 

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Yet Dana and the Jeep factory service manual recommend 75w140. I wouldn't put any stock in what a dealer tech has to say about anything.
This all day long. FCA has to meet CAFE requirements, Dana does not. There is no way I would run xW-80/85/90 in these axles.
 

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This all day long. FCA has to meet CAFE requirements, Dana does not. There is no way I would run xW-80/85/90 in these axles.
I don’t understand why anyone would run 75-90 when 75-140 isn’t going to “hurt” anything. In fact, it has a better chance to help protect the axle if you ever heat it up too much with towing or heavy loads. I bought a case of 75-140 and use it in both axles. Way easier that way.
 

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The factory service manual doesn't recommend 75w140. Page 15 a guy posted off the Stellantis service page. Only for the M200 does it say 75w140. I'm sorry, I guess all dealer techs are idiots. Only people that work at other garages or shade tree mechanics know what you're supposed to do. Hell, why don't we all run 10w30 in the engines like we used to instead of the 0w20 it recommends. I'm sure somewhere on the internet someone says they still use 10w30.
The change to lower viscosity oil has nothing to do with engine or axle longevity, it has everything to do with meeting CAFE requirements. In other countries, many engines run heavier viscosity oils in the same engines where the US specifies thin oil. There is a reason for that...
 

The Fixer

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Here's a few shots from today - my JL Sport has the M220 rear with Trac-Lok, 15K miles on it. Glad I did this today!

IMG_4344.JPG


IMG_4347.JPG


The oil was black as tar, with a nice little pile of stuff on the magnet as well. I think I will continue servicing the rear on my JL at 15K mile intervals, and the front at 30K. My wife's JLUS has the open M200 rear and we don't take it wheeling so I think I'll just do them both when it hits 30K.

And here's what I went with. The Flexfill pouches are amazing!

IMG_4342.JPG
 

omnitonic

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I'm sure somewhere on the internet someone says they still use 10w30.
Screw that. I run 20w50 and I add six pints of coal tar to the crankcase to improve cold flow. That's what my granddaddy did on his '43 Studebaker, and he lived to be 90 years old.
 

Heimkehr

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I don’t understand why anyone would run 75-90 when 75-140 isn’t going to “hurt” anything.
You might use the lighter oil if too many readings of the Owner's Manual has given you Analysis Paralysis.

That's exactly what I'm dealing with as I attempt to counsel a family member who's WK2 is due for fresh gear oil in both differentials. 75W-90 is specc'd for front and rear. Because, and only because, he asked me, I cogently explained the business case (as also mentioned multiple times in this thread) for using 75W-140 in the rear differential. And yet he's still waffling, the point that I'm ready to tell him to stop bothering me and just do whatever.


Screw that. I run 20w50 and I add six pints of coal tar to the crankcase to improve cold flow. That's what my granddaddy did on his '43 Studebaker, and he lived to be 90 years old.
There's a place for 20W-50 in this modern world of ours, lol. The dual hydrostatic drives on my zero turn mower require mineral 20W-50 for each service interval. That oil is also the required weight for the Ural's engine when ambient temps are above 50°F. I used 20W-50 when I owned my MGB, too; loose build tolerances for the Win.

And so I've a small stock of a not-so-outdated engine oil on the shelf. No coal tar, though...
 

omnitonic

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I used 20W-50 when I owned my MGB, too; loose build tolerances for the Win.

And so I've a small stock of a not-so-outdated engine oil on the shelf. No coal tar, though...
You need to add coal tar, some turpentine, a little bit of Mercurochrome, and some asbestos. Asbestos helps the oil lubricate properly in those sloppy British engines.

But seriously, I'm struggling with some analysis paralysis of my own. I got a shop to regear my Jeep to 4.56, which worked out great. I was going to let the shop guy do the 500 mile service, but he didn't answer his phone when I called to set it up.

If he can't be bothered to answer the phone, I can't be bothered to burn half a day driving to his shop. I'm going to do it myself.

I'm on the fence. Yukon recommends conventional 80w90. I have a jug of conventional 80w90, but I would need to go buy some friction modifier for my LSD. I also have a jug of synthetic 75w90 that already includes a suitable friction modifier, and "Valvoline recommends SynPower 75w90 for limited-slip differentials."

Yukon made the gears, so I should go with Yukon's recommendation. But gears is gears is gears.

I think I'm going to go with the 75w90 synthetic, but researching this topic makes my head ache.
 

CarbonSteel

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You need to add coal tar, some turpentine, a little bit of Mercurochrome, and some asbestos. Asbestos helps the oil lubricate properly in those sloppy British engines.

But seriously, I'm struggling with some analysis paralysis of my own. I got a shop to regear my Jeep to 4.56, which worked out great. I was going to let the shop guy do the 500 mile service, but he didn't answer his phone when I called to set it up.

If he can't be bothered to answer the phone, I can't be bothered to burn half a day driving to his shop. I'm going to do it myself.

I'm on the fence. Yukon recommends conventional 80w90. I have a jug of conventional 80w90, but I would need to go buy some friction modifier for my LSD. I also have a jug of synthetic 75w90 that already includes a suitable friction modifier, and "Valvoline recommends SynPower 75w90 for limited-slip differentials."

Yukon made the gears, so I should go with Yukon's recommendation. But gears is gears is gears.

I think I'm going to go with the 75w90 synthetic, but researching this topic makes my head ache.
Remember that lower gear ratio you have (higher numerical value), the higher the operating temperature. If you are in a hot climate, have heavier loads, or run for extended times, you will want additional protection, i.e, 75W-140.

There is no negative to upping the viscosity...
 
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