Just regeared to 4.56…best diff fluid to use and why?

[MiddleClassHero]

I have 2020 JLU Sport (2.5” lift/35” tires) which was just regeared to 4.56 (revolution gears) and am coming up on my first 500 miles post regear.

My jeep is garage kept and a daily driver that doesn’t get much off road action, so I wanted to know what the best diff fluid is to use for the front and rear diffs and why? Thanks in advance for the response and recommendations!

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[chevymitchell]

I have 2020 JLU Sport (2.5” lift/35” tires) which was just regeared to 4.56 (revolution gears) and am coming up on my first 500 miles post regear.

My jeep is garage kept and a daily driver that doesn’t get much off road action, so I wanted to know what the best diff fluid is to use for the front and rear diffs and why? Thanks in advance for the response and recommendations!

Use what MOPAR recommends (Owners Manual)

or

75w90 Valvoline Full Synthetic - Front
75w140 Valvoline Full Synthetic - Rear

There is nothing special about a differential to where one fluid will matter more than what the MFG recommends. Just remember to get friction modifier or fluid that has it mixed in if you have limited slip.

I've used them all: Royal Purple, AMSOIL, Valvoline, MOPAR, etc... You won't be able to tell a performance difference from the seat. Some will sheen better than others and some will control temp better than others but for your use case, there is no need to go above and beyond what is in your Owners Manual.

 

[azwjowner]

I am running cheap conventional 85w140 for the next 5000 miles after my 500 mile change, then Amsoil 75w140 from then on.

 

[MiddleClassHero]

Use what MOPAR recommends (Owners Manual)

or

75w90 Valvoline Full Synthetic - Front
75w140 Valvoline Full Synthetic - Rear

There is nothing special about a differential to where one fluid will matter more than what the MFG recommends. Just remember to get friction modifier or fluid that has it mixed in if you have limited slip.

I've used them all: Royal Purple, AMSOIL, Valvoline, MOPAR, etc... You won't be able to tell a performance difference from the seat. Some will sheen better than others and some will control temp better than others but for your use case, there is no need to go above and beyond what is in your Owners Manual.

Use what MOPAR recommends (Owners Manual)

or

75w90 Valvoline Full Synthetic - Front
75w140 Valvoline Full Synthetic - Rear

There is nothing special about a differential to where one fluid will matter more than what the MFG recommends. Just remember to get friction modifier or fluid that has it mixed in if you have limited slip.

I've used them all: Royal Purple, AMSOIL, Valvoline, MOPAR, etc... You won't be able to tell a performance difference from the seat. Some will sheen better than others and some will control temp better than others but for your use case, there is no need to go above and beyond what is in your Owners Manual.

Thanks for the response. The owners manual says 75w85 but I figured that’s for the stock gears 3.45.

What is the benefit of going up to to 75w90 for the front and 75w140 for the rear and are those better for bigger gears like 4.56?

 

[chevymitchell]

Thanks for the response. The owners manual says 75w85 but I figured that’s for the stock gears 3.45.

What is the benefit of going up to to 75w90 for the front and 75w140 for the rear and are those better for bigger gears like 4.56?

Size of the gear really doesn’t matter.

The rear is the most important for raising the viscosity. Once you modify your Jeep and you end up with a net weight gain over stock around 300-1000 lbs, depending on mods; you’re basically towing all the time. This is why I have always recommended the severe duty use viscosity for anything lifted, bigger tires, racks, whatever else you add that’s significant in net weight gain.

75w90 is easily obtainable just about anywhere and the front ring and pinion aren’t building heat unless in 4WD under load.

75w140 is the severe duty recommendation.

 

[Jeep Wick]

Thanks for the response. The owners manual says 75w85 but I figured that’s for the stock gears 3.45.

What is the benefit of going up to to 75w90 for the front and 75w140 for the rear and are those better for bigger gears like 4.56?

It's safe to run 75w140 both front and rear. If you're going to keep it long term, that's what I would recommend.

 

[MiddleClassHero]

Size of the gear really doesn’t matter.

The rear is the most important for raising the viscosity. Once you modify your Jeep and you end up with a net weight gain over stock around 300-1000 lbs, depending on mods; you’re basically towing all the time. This is why I have always recommended the severe duty use viscosity for anything lifted, bigger tires, racks, whatever else you add that’s significant in net weight gain.

75w90 is easily obtainable just about anywhere and the front ring and pinion aren’t building heat unless in 4WD under load.

75w140 is the severe duty recommendation.

Makes sense. Thanks for the help!

 

[Bill_BCNtoNY]

It's safe to run 75w140 both front and rear. If you're going to keep it long term, that's what I would recommend.

I ended up doing just this back when I re-geared to 4.56:

 

[Jeep Wick]

I ended up doing just this back when I re-geared to 4.56:

I too am a big Mobil 1 fan.

 

[bobholthaus]

Any issue with cold weather with the 75w140 fluid? Someone told me that it can get too thick in cold weather.

 

[jbcrane]

Any issue with cold weather with the 75w140 fluid? Someone told me that it can get too thick in cold weather.

Bob, I run 75W140 front and rear (4.88's) and am in Colorado. It has been below 0 here for a while, today in the 20's. No issues what so ever.

I'm no expert, but I don't know how an oil being too thick (up to a certain point) would hurt a differential. Once it's turning and builds heat, viscosity changes allowing oil to flow where designed. It's not like an engine – where on cold start, for example – oil needs to be pressurized and pumped to get into every little nook and cranny of the engine to be properly lubricated.

Thinner gear oil – I believe (like thinner engine oil) – is spec'd more for increased mileage across many vehicles. Someone correct me if I'm wrong.

 

[bobholthaus]

Bob, I run 75W140 front and rear (4.88's) and am in Colorado. It has been below 0 here for a while, today in the 20's. No issues what so ever.

I'm no expert, but I don't know how an oil being too thick (up to a certain point) would hurt a differential. Once it's turning and builds heat, viscosity changes allowing oil to flow where designed. It's not like an engine – where on cold start, for example – oil needs to be pressurized and pumped to get into every little nook and cranny of the engine to be properly lubricated.

Thinner gear oil – I believe (like thinner engine oil) – is spec'd more for increased mileage across many vehicles. Someone correct me if I'm wrong.

This makes logical sense to me. I can't imagine that once the diff is moving, whether under a towing load or not, that it heats up very quickly. Thank you!

 

[Gunfighter]

Any issue with cold weather with the 75w140 fluid? Someone told me that it can get too thick in cold weather.

No. The Jeep drives fine, It's been in a zone of -10°F to 105°F.

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