5000 miles Front/Rear diff fluid + T-case fluid check results

LTZ470 said:
From my 2018 JL Sahara Jeep Manual: Doesn't say 75W-140 at all for the M220 = Dana 44 HD......window sticker attached for review...I can say this with FULL confidence as well as soon as I put the Royal Purple 75W-140 in the Dana HD44 it ran MUCH quieter and did not "pop" near as much as it did with 85W-90 + Friction Modifier...the Royal Purple 75W-140 does not require Friction Modifier...
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Trust me I believe 75w-140 is better in every way for any rear axle, I have that in every vehicle I own, 4 of them, except the 392. And my warranty will be up in about 10 months and then it will be swapped From 80-90 to 75w-140
 
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LTZ470 said:
From my 2018 JL Sahara Jeep Manual: Doesn't say 75W-140 at all for the M220 = Dana 44 HD......window sticker attached for review...I can say this with FULL confidence as well as soon as I put the Royal Purple 75W-140 in the Dana HD44 it ran MUCH quieter and did not "pop" near as much as it did with 85W-90 + Friction Modifier...the Royal Purple 75W-140 does not require Friction Modifier...
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This is the page from the 2018 manual.
IMG_0266.webp
 
This page is from my 2018 JL Manual:
Screenshot 2023-06-14 at 18.41.46.webp
 
stumblinhorse said:
Well that is strange for 2 reasons, you can’t put ATF+4 in your manual transmission nag-370…
And it doesn’t mention the sales code. But the picture I posted if from the Jeep owners site.

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www.jlwranglerforums.com

What manual transmission fluid are you using?

The manual calls for Mopar ATF+4 for transmission and transfer case. On my JK I used synchromesh for the transmission and Mopar ATF+4 for the transfer case. I liked synchromesh but don't know if that's still ok for the JL.
www.jlwranglerforums.com www.jlwranglerforums.com
 
Diff fluid was a little sludgy at 4K miles. Replacement transfer case was actually topped off.

IMG_1897.webp

IMG_1898.webp

IMG_1896.webp
 
Fast-n-Furious said:
Looks good at 4k. Mine was very dark at 7.5k. I used yellow teflon tape since it’s oil resistant and much ticker.
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Yellow tape just lets someone know you paid more for it. Same as blue, purple, grey or green. You can buy any of them in any thickness you want. They are all oil resistant. Even the super thin white stuff you buy from home Depot. All are rated for fuel oils, natural gas, lpg, etc. Some just aren't rated for threads over 1-1/2". That's a whole other category though.
 
My 2024 392 owners manual says for M220 real diff to use 75w85 with friction modifier. Sales code M200 uses the thicker 75w140. What Jeeps have sales code M200?

I wish we really knew why Jeep calls for that when the Spicer Dana website says use 75w140…??? Very confusing info here.
 
MDrums said:
My 2024 392 owners manual says for M220 real diff to use 75w85 with friction modifier. Sales code M200 uses the thicker 75w140. What Jeeps have sales code M200?

I wish we really knew why Jeep calls for that when the Spicer Dana website says use 75w140…??? Very confusing info here.
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Use the synthetic 75W140…that’s what I use, Spicer-Dana built the axles….
https://media.spicerparts.com/cfs/files/media/fw8jLykPD9RGpxSct/SPECSHEET-JL-FRONT-UD44A-42019.pdf?token=eyJhdXRoVG9rZW4iOiIifQ==&store=original

 
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MDrums said:
My 2024 392 owners manual says for M220 real diff to use 75w85 with friction modifier. Sales code M200 uses the thicker 75w140. What Jeeps have sales code M200?

I wish we really knew why Jeep calls for that when the Spicer Dana website says use 75w140…??? Very confusing info here.
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Yes it is confusing. Especially where you are trying to maintain a warranty. When there is no mopar document that recommends 75w140 for the axles in the 392. In the same document it does recommend that for m200s.
 
Thanks... I am only at 200 miles... I will probably wait to change before this summer...late spring around 4k miles I guess.

I want to check my fluid level so I guess I'll buy a bottle of whatever brand Lucus or Mobil 75w85 incase I need to top off the diffs?????
 
MDrums said:
Thanks... I am only at 200 miles... I will probably wait to change before this summer...late spring around 4k miles I guess.

I want to check my fluid level so I guess I'll buy a bottle of whatever brand Lucus or Mobil 75w85 incase I need to top off the diffs?????
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Friction Modifier is for Limited Slip Axles (Sahara), not required in Rubicon Open/Locking Differentials....392 applies excessive torque on these M220 Axles, 75W140 Synthetic gives you extensively more wear protection than 85W90 especially if you pull a trailer and are also located in warmer climates...75W140 will not void your warranty unless Mopar can prove it damaged your Jeep axle which it will not...some dealers are actually replacing the 85W90 with 75W140 Synthetic...

Common sense is not so common any more for sure...the struggle is real....
 
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LTZ470 said:
Friction Modifier is for Limited Slip Axles (Sahara), not required in Rubicon Open/Locking Differentials....392 applies excessive torque on these M220 Axles, 75W140 Synthetic gives you extensively more wear protection than 85W90 especially if you pull a trailer and are also located in warmer climates...75W140 will not void your warranty unless Mopar can prove it damaged your Jeep axle which it will not...some dealers are actually replacing the 85W90 with 75W140 Synthetic...

Common sense is not so common any more for sure...the struggle is real....
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I have said it before it is funny where people will say I would never use xxx it would void my warranty. There are several things that are ridiculous in the 392 fluids that are ridiculous. 1 is the requirement to change out the required synthetic engine oil every 6 months, for my 392 that is 1500-2000 miles. That is ridiculous. 2nd is the requirement to run 75w90 with no mention of towing etc and 75w140. The 3rd is the owners manual says brake fluid for 2021 392 is SAE J1709, that brake fluid is a spec from Europe 15 yrs ago…. All ridiculous and stupid. But dealers are more ridiculous and stupid when they tell people ”to return the Jeep to stock to see if the problem persists“
 
MDrums said:
My 2024 392 owners manual says for M220 real diff to use 75w85 with friction modifier. Sales code M200 uses the thicker 75w140. What Jeeps have sales code M200?

I wish we really knew why Jeep calls for that when the Spicer Dana website says use 75w140…??? Very confusing info here.
Click to expand...
Yeah my 2022 392 Performance guide calls for 75w85, so that's what I use. I think the OEMs specify that lower viscosity 75w85 gear oil for improved CAFE fuel economy numbers. Same idea as MDS, it's not ideal from an engineering point of view but fuel economy improvements are cumulative. Lots of little compromises like using 75w85.
IMG_1801.jpeg

To make this job more 'fun' I went out and splurged on a new Harbor Freight Icon creeper with a pair of Braun 750 Lumen rechargeable magnetic lights which was a huge improvement over some brakedancing cardboard on the floor. The creeper is comfy and rolls well, maybe even too wellllllll...... I used my GoJack dollies to lift the four wheels and I checked the T-case, it was 300ml (⅓ qt low) which is about 15% below the standard. The diffs were just about on the mark, maybe 50ml low. I use Permatex 59235 High Temp Thread Sealant which is what the OEM uses to seal the plugs. Thanks @KuntryRube for the tip to check the transfer case!

After checking fluids I sprayed 4 cans of Blaster Surface Shield to prevent rust. This is my second time spraying the frame and I probably could have skipped it but I went ahead anyways. It's kinda like seasoning a cask iron skillet, each layer of lanolin builds up a barrier. I was very impressed with how well it has held up from last fall. I went ahead and wiped off a spot and the frame looks brand new underneath. In my experience rust is what kills Jeeps. Let it snow! ☃️

IMG_1803.jpeg

 
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stumblinhorse said:
I have said it before it is funny where people will say I would never use xxx it would void my warranty. There are several things that are ridiculous in the 392 fluids that are ridiculous. 1 is the requirement to change out the required synthetic engine oil every 6 months, for my 392 that is 1500-2000 miles. That is ridiculous. 2nd is the requirement to run 75w90 with no mention of towing etc and 75w140. The 3rd is the owners manual says brake fluid for 2021 392 is SAE J1709, that brake fluid is a spec from Europe 15 yrs ago…. All ridiculous and stupid. But dealers are more ridiculous and stupid when they tell people ”to return the Jeep to stock to see if the problem persists“
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Yes sir I am with you on that, I didn't change my 8.9L Cummins oil for 5 years, the samples had no water in them, and the oil was still in good condition when changed...I'm sure some additives can break down overtime, but no issues have I observed...

392 Manual also states in dusty conditions change each 4000 miles...

After observing the fine metal filings or "swarf" when changing my 392 rear axle oil, 75W140 was a MUST...in time it will prove to be the right choice, with these high torque engines it is the only choice....

Jeep is sometimes guilty of selling the king new clothes....

Dana/Spicer no doubt recommends 75W140 for "their" Dana 44 Axles in the Jeep 392 for "longevity"...that says it all to me...I'll take longevity over any other smoke and mirror explanation Jeep has....
 
My two cents on 75w140:

I swapped out the diffs on my 4runner with units from East Coast Gear. East Coast specifically required Lucas 85w140 for their units or they would not honor the warranty. It's been a while since then, but I remember speaking to one of their reps about it and he said larger tires and increased loads called for the higher weight rating to be used. I put that in the 4runner and it was perfectly fine.

I'm certain that Jeep calls for the lower weight rating to bump the fuel economy a tiny bit.

We all have 392's with tons of HP and Torque and most of us have 35's or larger tires. I'd say the 85w140 is a sensible way to go and I don't think it's ever going to cause a failure. If you don't agree, use whatever you like. For me, East Coast sets up and sells thousands of diffs every year. I trust their opinion.

One thing to note about the suggested things from Manufacturer Engineers: If you get a 60,000 mile power train warranty, that's their target. For example, if you ask a Chrysler Engineer "if we change the oil every 10,000 miles, will the engine last through the 60,000 mile warranty most of the time" they will say yes. THEN ask "how often should we change the oil to make it to 100,000 miles most of the time" they will probably say, change the oil a lot more frequently...

Here's a link to a 3 page recommendation from ECGS that gets into the details on Temp, Cling and Water in the oil. This is a great read for sure. https://eastcoastgearsupply.com/files/PDF Files/ecgs-gear-oil-recommendation1.pdf
 

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Since the 392 is always 4 auto or 4h or 4l would it hurt anything to only use 75w/140 in the rear axle and leave the front axle fluid stock?
 

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