What 80w-90 front diff gear oil are you using??

[CarbonSteel]

I would run 75W-110 in the front axle because it is the upper viscosity 75W-90 used to be before the SAE J306 tables were updated. I have had fantastic service with Amsoil gear oil and would highly recommend it. I would also recommend changing the rear axle oil at 10K miles. The vast majority of all axle wear occurs in the first 15K of use. I have seen this repeatedly in every axle I have ever owned and have UOA data to support it as well.

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[JIMBOX]

I will only use VALVOLINE 75W-140 SYN. in both Diffs--have for decades--suits me fine-

W.E.

JIMBO

 

[Poromenos]

RP 75-90 in both. Switched at 20k.

 

[wheels082]

Amsoil Severe Gear 75w90.
https://www.amsoil.com/shop/by-product/gear-lube/severe-gear-75w-90/?code=SVGPK-EA/?zo=226468

 

[oceanblue2019]

Royal Purple 75W/90 in the front, 75W/140 in the rear.

 

[wheels082]

When I had my JK re-geared the shop told me I could run any gear oil I wanted except Royal Purple. They said they see an increase in wear inside the diffs when people use it.

 

[DanW]

When I had my JK re-geared the shop told me I could run any gear oil I wanted except Royal Purple. They said they see an increase in wear inside the diffs when people use it.

I find that to be odd. It meets the API specs for GL5 or GL4 and has a strong base oil, so there's really no reason for that to be the case. Sounds like a mechanic's wives tail, to me. I've had mechanics that swear by Valvoline tell me Pennzoil was terrible and vice versa. Many times, that stuff doesn't make sense. I see nothing in the product data sheet that is significantly different from other synthetics.

 

[jeepdabest]

I changed mine at 16k and it looked perfect. T-case fluid is ATF+4. Chrysler transmissions typically recommend 100k changes for auto trannys using ATF+4. The transfer case gets MUCH less wear and tear than a transmission. So why did I do it? It was cheap, I like getting break-in crap out, and I was heading to Moab soon after. It just made me feel better. I used NAPA ATF+4 which is very cheap and made by Valvoline.

As for diffs, synthetic 75w90 has 80w90 completely covered. There is no issue in substituting it. It will out perform 80w90 at every temperature. The viscosity difference would be barely noticeable in a lab, and probably completely unnoticeable to the naked eye or the touch, except at 30 below zero, where the 80w90 would flow like chewing gum.

As said before, the front diff gets barely any wear because most of the time it has no working load on it. The axles turning cause next to no stress. Either the 75 or 80 GL5 will make it outlast the rest of the Jeep if you keep it topped off.

Change it early to feel good, or change it by the book and you can still feel good. For me, I'll change it more often because I like to tinker with my Jeep.

I've currently got Valvoline synthetic in both ends, with 75w140 in the rear. I changed it, too, at 16k and the fluid looked good, but had plenty of wear metal on the magnet. I did have 75w90 in the rear for the trip to Moab. I had it laying around. I swapped it to the 140 when I returned home. The 140 is recommended for towing, which I do, but didn't do on that trip. There was very little wear metal on the magnet after the trip. Almost none. I only ran a few thousand miles on it.

Would 75w140 rear be harmful if you DON'T tow?

 

[DanW]

Would 75w140 rear be harmful if you DON'T tow?

Nope. It wouldn't hurt a thing.

 

[jeepdabest]

Nope. It wouldn't hurt a thing.

Thank you!

 

[wheels082]

Would 75w140 rear be harmful if you DON'T tow?

There would be a small reduction in fuel economy compared to a 75w90/80w90. If you live in a place that gets cold winters I would not use a conventional 75w140.

 

[DanW]

There would be a small reduction in fuel economy compared to a 75w90/80w90. If you live in a place that gets cold winters I would not use a conventional 75w140.

I doubt you'd even be able to measure the mpg difference and when cold, it has the same kinematic viscosity, this the 75w, so again, there would be no functional or perceptible difference, IMO.

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