Differential oil change

[nU7OuxIx]

Yes, you are correct. The second number is at typical operating temperature and the first number is when cool. For motor oil, the operating temp viscosity would be 212 degrees. I'm not sure if they use the same number for gear oil, but they probably do to keep it a standard viscosity measurement. The idea of the 90 instead of 140 would indeed be to have less resistance at operating temperature, and thus, generate very slightly better fuel economy. Even the automakers don't expect the number to be noticeable but if they do a number of different things, such as gear oil, engine oil, and who knows what else, they might see two tenths of an MPG. When you make millions of vehicles, that number makes a difference. To an individual, it means nothing and they'd never know it.

I also read that thicker oil can introduce bubbles, and the gears prefer oil instead of air.

Is this a myth? My eyebrow is a bit raised about this one, as I can't really see this happening. Or if it happens, not enough where it would damage anything.

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[DanW]

I also read that thicker oil can introduce bubbles, and the gears prefer oil instead of air.

Is this a myth? My eyebrow is a bit raised about this one, as I can't really see this happening. Or if it happens, not enough where it would damage anything.

Myth. While Jeep recommends the lighter gear oil both front and rear (non towing), Dana recommends 75w140 in both. Dana has no worries about fuel economy.

But 75w90 would do just fine, especially in the front, which doesn't work hard. If you tow, though, you definitely want 75w140 in the rear.

I've been running 75w140 rear and 75w90 front, but after re-gearing and dumping the break-in oil I've now got 75w140 in both ends.

My wife's JLUR will hit 15k this summer. I'll be doing the same with it, even though she doesn't tow.

 

[Mightyoak]

Im almost at 20,000 miles so I think I should change the diff oil too. Did you use thread sealer? Is the Valvoline working well? Does it have enough friction modifier? I worry to much about everything.

I did use thread sealer the yellow one. Working great so far!

 

[Paluss]

Did my 2nd Diff fluid change on my 2018 JLUR, I did the first change at 25k (rear only), and I am at 49k so I did the 2nd (both front and rear). The rear fluid was dark (similar to 25k) front was still an amber color (I only use 4wd during the small amount of snow we get in Maryland). both drain plugs were clean with a bit of almost a paste (no metal filings) on it. Just sharing YMMV

 

[waypoint]

2021 JLUS with limited slip rear, 13K miles and I just changed the rear diff fluid. Factory fluid was dark brown but still translucent as it drained, minor metal paste w/ some fine fuzz on the drain plug magnet. Amsoil Severe Gear 75W-140 and 1/3 bottle of Mopar LSD additive as the Amsoil has friction modifier additive included. ARP thread sealant (white paste) on the plugs. Very glad for the drain plug on the diff housing and no need to pop the cover. Test drive was smooth including sharp cornering at low speed to test the differential function, no chattering.

 

[jjvincent]

I'm going with Redline Shockproof Blue. Why? I live in the world of motorsports and that stuff works quite well. Plus it does lower diff temps (as we log with data). The Jeep diff is nothing special (just some sort of Dana (insert number here).

 

[myexcursion]

I have a 2019 JLU Sahara 3.6 but it does not have the LSD. Do i just pick up Valvoline or Amsoil 75w140 in both front and rear and call it a day ? Do I need to add any modifier or sealant thread ?

 

[CarbonSteel]

I have a 2019 JLU Sahara 3.6 but it does not have the LSD. Do i just pick up Valvoline or Amsoil 75w140 in both front and rear and call it a day ? Do I need to add any modifier or sealant thread ?

Good to go with Valvoline off the shelf. Nothing else needed.

 

[Chupacabra]

2021 JLUS with limited slip rear, 13K miles and I just changed the rear diff fluid. Factory fluid was dark brown but still translucent as it drained, minor metal paste w/ some fine fuzz on the drain plug magnet. Amsoil Severe Gear 75W-140 and 1/3 bottle of Mopar LSD additive as the Amsoil has friction modifier additive included. ARP thread sealant (white paste) on the plugs. Very glad for the drain plug on the diff housing and no need to pop the cover. Test drive was smooth including sharp cornering at low speed to test the differential function, no chattering.

Why are you adding additional LSD additive to gear oil that already has it?

 

[waypoint]

Why are you adding additional LSD additive to gear oil that already has it?

My prior experience with Amsoil Severe Gear in other clutch-type LSDs has been that more additive was needed. 1/3 of the 8oz bottle seemed like a good starting point. May be unnecessary but can't hurt.

 

[word302]

My prior experience with Amsoil Severe Gear in other clutch-type LSDs has been that more additive was needed. 1/3 of the 8oz bottle seemed like a good starting point. May be unnecessary but can't hurt.

Actually you don’t want more friction modifier than you need.

 

[Chupacabra]

My prior experience with Amsoil Severe Gear in other clutch-type LSDs has been that more additive was needed. 1/3 of the 8oz bottle seemed like a good starting point. May be unnecessary but can't hurt.

Well, wouldn't too much additive basically turn your LSD into an open diff? I'm not sure that it "can't hurt" but it's your diff

 

[smokeythecat]

I love these threads that are mostly anecdotal accounts with no data. That way you just get to look through all the posts until you see something that confirms what it is you already wanted to do.

 

[CarbonSteel]

Well, wouldn't too much additive basically turn your LSD into an open diff? I'm not sure that it "can't hurt" but it's your diff

It can and will hurt--too much additive will cause the clutches to slip more than they should and therefore it will perform as an open differential.

Start with whatever is already in the oil. Drive it for about 25 miles, then get into a parking lot and slowly make several figure 8's while listening for popping or chattering.

If you hear those noises when making the turns, then add a small amount of additive and re-test. Repeat if necessary, but stop when the noise stops.

From my experience, I have only had 1 axle need more additive versus what was already in the oil

 

[rcadden]

Read this whole thread and I feel *mostly* confident, but there's a lot of opinions and little data.

I have a '21 Sahara with LSD + tow package. It's my daily driver, and I get it out for light wheeling maybe once/quarter (which sucks, but that's another topic). Don't really tow (got the package for the aux switches really).

Just hit 20K miles.

Watched a video on how to do it - seems easy enough. Will make sure I have yellow teflon tape and 2qts of fluid, but which fluid?

90 - mostly recommended, listed in the service manual?
140 - better protection cause it's thicker, but not entirely necessary. Might drop my MPG slightly.

Leaning toward the Valvoline flex fill 140 for both front/rear. Royal Purple is ~$5/qt more - worth it for my usage?

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