75W-90 vs 75W-140

[djnelson5460]

Hi all. Quick question. I have an ‘18 1500 with the open diff and 3.23 gears. It calls for 75W-140, however the same truck with limited slip calls for 75W-90. Is that only because of the limited slip clutches thats its a lighter wieght? If I put in the 75W-90 in my open diff will it hurt anything, or give it better MPG? Thanks, hope you had a Happy New Year

 

[caulk04]

Guess I'll need to revisit my manual, I thought mine called for 75w140 in my lsd equipped 18. Would be nice, since I have 4qt of amsoil on hand.

My opinion is that if you aren't going to tow often or near capacity, you'll be fine with the thinner fluid. I gave the same advice through my previous Jeep platform where they all called for 75w140 but was likely only needed in the upper trim levels with electrohydraulic lockers.

 

[crash68]

The 1500s use 75W-140 in the rear 75W-90 in the front, doesn't matter if the truck has LSD or not. If your towing or hauling with your truck, I doubt there will be any problems running 75W-90 in the rears also.

It's the HD trucks that use 75W-90 front and rear, those also don't need a friction modifier as the use a helical gear LSD.

 

[djnelson5460]

Cool thanks for the info guys

 

[pacofortacos]

A good compromise if you do haul or tow anything is a 75-110 gear oil, the thinner oils will help below freezing.
I don't know if I noticed a mpg difference (since I only drive the truck seldom and usually for decent distances), but I did notice more of a drag pulling out cold with the 75-140.

 

[Different Drummer]

Here is something to ponder. My manual states 75W-140 with friction modifier added due to LSD. I had the dealer do a Diff. fluid change before a cross country trip and stressed he use the 75W-140. After 300 miles into the trip I started experiencing what was obviously behavior caused by NO friction modifier being added. . Called dealer, they looked up service order and sure enough , no LSD additive used. In the conversation he stated that Diff. called for 75W-90. I had little lady get the manual out as we were driving and had dealer on the phone. Manual states 75W-140. OK, so I have to find a dealer to put the additive in. Dealer I find is very accommodating and takes me right in. He also states Diff. called for 75W-90. I show him my manual that says 75W-140. He checks with parts Dept. They say 75W-90. They let me call FCA customer assistance and they say 75W-90. But of course they are just some guy looking it up on the computer. Everyone agrees that the 75W-140 will do no harm, but I certainly do not need it with the service the truck see's.
Both dealers were using VIN to research proper fluid.

Note: My truck is 2017, 2WD with LSD 3.21 ratio
I have not had any problems since having the friction modifier added.

 

[WY-Dave]

The ratings for gear oil is hot and cold range.
Tthe first number of a multigrade oil, preceding the W(Winter NOT Weight like in motor oil), is the performance at 0°C while the second number rates it’s performance at 100°C.

The idea of multiviscosity oils isn't to get thicker at higher temps - it's to MAINTAIN viscosity at the higher temps.

 

[djnelson5460]

Gotcha, thanks all for the info. I dont do any heavy towing/hauling, or drag racing haha, so I’ll go with the 90 weight on my next fluid change, and make sure I get as much of the 140 out of there as physically possible

 

[Different Drummer]

Gotcha, thanks all for the info. I dont do any heavy towing/hauling, or drag racing haha, so I’ll go with the 90 weight on my next fluid change, and make sure I get as much of the 140 out of there as physically possible

We're neighbors and I am not losing any sleep over the 75W-140 presently in my Diff.

 

[pacofortacos]

Front actually call for a 75-85 gear oil but the 75-90 will work.

 

[djnelson5460]

Yeah I figured 90 compared to 85 in the front wasnt that big a deal, just didnt know about the rear

 

[sirdumpsalot]

Here is something to ponder. My manual states 75W-140 with friction modifier added due to LSD. I had the dealer do a Diff. fluid change before a cross country trip and stressed he use the 75W-140. After 300 miles into the trip I started experiencing what was obviously behavior caused by NO friction modifier being added. . Called dealer, they looked up service order and sure enough , no LSD additive used. In the conversation he stated that Diff. called for 75W-90. I had little lady get the manual out as we were driving and had dealer on the phone. Manual states 75W-140. OK, so I have to find a dealer to put the additive in. Dealer I find is very accommodating and takes me right in. He also states Diff. called for 75W-90. I show him my manual that says 75W-140. He checks with parts Dept. They say 75W-90. They let me call FCA customer assistance and they say 75W-90. But of course they are just some guy looking it up on the computer. Everyone agrees that the 75W-140 will do no harm, but I certainly do not need it with the service the truck see's.
Both dealers were using VIN to research proper fluid.

Note: My truck is 2017, 2WD with LSD 3.21 ratio
I have not had any problems since having the friction modifier added.

I have a 2017 1500 4xd, LSD, 3.55, my owner's manual says 75w90 in the rear, but apparently other manuals will say 75w140...

I do frequently tow a 5k travel trailer, sounds like 75w140 is the way to go despite what the owner's manual says?

 

[Jwithing]

FYI, just changed my diff fluid and according to Nick from GotExhaust, the redline gear oil already has the necessary additive for LSD. 5K miles or so since my fluid change and no issue. I used the 140.

 

[Burla]

Why differ from the manual on something like gear oil? 75w140 for the rear. Consider that ever single crazy idea for fuel mileage and your manu absolutely does, vvt, mds, thin trans oil, thin engine oil, pre heated transmission oil in late rfe's and 8 speeds, adding gears to transmission, etc etc, and despite heavy oil giving less mpg's and they go out of their way to recommend 140w oil for their diff and you would "rather" run 90 weight? Plus they go out of their way to recomend two different oil weights for both diifs and that also does not give you pause?

From your manual...

Front Axle – 1500 Four-Wheel Drive Models We recommend you use Mopar GL-5 Synthetic Axle Lubricant SAE 75W-85.

Rear Axle – 1500 Models We recommend you use Mopar Synthetic Gear Lubricant SAE 75W-140 (MS-8985). Limited-Slip Rear Axles require the add.....

75w85 has a visc around 12, similar to 5w30 engine oil.

75w90 has a cSt viscosity of around 16.

75w140 has a cSt viscosity around 27.

Not saying what oil you should use, just posting up info so you have more info, if you decide on something else, hopefully it works out.

 

[MontanaHandyman]

Why differ from the manual on something like gear oil? 75w140 for the rear. Consider that ever single crazy idea for fuel mileage and your manu absolutely does, vvt, mds, thin trans oil, thin engine oil, pre heated transmission oil in late rfe's and 8 speeds, adding gears to transmission, etc etc, and despite heavy oil giving less mpg's and they go out of their way to recommend 140w oil for their diff and you would "rather" run 90 weight? Plus they go out of their way to recomend two different oil weights for both diifs and that also does not give you pause?

From your manual...

Front Axle – 1500 Four-Wheel Drive Models We recommend you use Mopar GL-5 Synthetic Axle Lubricant SAE 75W-85.

Rear Axle – 1500 Models We recommend you use Mopar Synthetic Gear Lubricant SAE 75W-140 (MS-8985). Limited-Slip Rear Axles require the add.....

75w85 has a visc around 12, similar to 5w30 engine oil.

75w90 has a cSt viscosity of around 16.

75w140 has a cSt viscosity around 27.

Not saying what oil you should use, just posting up info so you have more info, if you decide on something else, hopefully it works out.

Y'know, I've always wondered why the front diff would be spec'd for a lighter weight gear oil?? Cuz it might be used more in winter when it's colder??

 

[Docwagon1776]

Y'know, I've always wondered why the front diff would be spec'd for a lighter weight gear oil?? Cuz it might be used more in winter when it's colder??

Just a guess, but likely because it never sees 100% of the vehicle's output. The rear always gets used and gets the full power available. The front only sees partial load when used.

Complete guess, though.

 

[HEMIMANN]

Just a guess, but likely because it never sees 100% of the vehicle's output. The rear always gets used and gets the full power available. The front only sees partial load when used.

Complete guess, though.

Correct.

You can see an example of a full time 4WD truck by looking at an Oshkosh truck for the military or airport maintenance.

 

[slickracer]

Guess I'll need to revisit my manual, I thought mine called for 75w140 in my lsd equipped 18. Would be nice, since I have 4qt of amsoil on hand.

My opinion is that if you aren't going to tow often or near capacity, you'll be fine with the thinner fluid. I gave the same advice through my previous Jeep platform where they all called for 75w140 but was likely only needed in the upper trim levels with electrohydraulic lockers.

My 2018 LSD calls for 75W-90 in the owners manual.

 

[djnelson5460]

My 2018 LSD calls for 75W-90 in the owners manual.

What is your gear ratio, 3.23 or 3.92?

 

[slickracer]

From 194-210, with an average of 203. Took it to the dealership, no issues. Thought the coolant was low and they ran a pressure test, nothing. They filled it back up and its fine, but its always had the temperature fluctuations, along with everyone else I have asked.

What is your gear ratio, 3.23 or 3.92?

3.21