Differential Oil for Off Road use and Hot Climate

[knightjp]

I live in the Middle East where the temps during Summer average 50.C
I'm told by ChatGPT that the standard differential oil for my 2014 Ram 1500 is:
SAE 75W-85 GL-5 in the front
SAE 75W-140 GL-5 in the rear (Mopar spec MS-8995).
I'm sure that I can get the original Mopar brand oil, however I was wondering if there were any tips in terms of oil brand, viscosity and change intervals; especially for those who live in my kind of climate.

For instance, brands like Valvoline over here only stock 80W-90 and 85W-140. Are these also acceptable?

How often should the diff oil be changed?

 

[Curmudgeon]

Without looking it up, IIRC diffs are every 30k and transfer case is 60k.
Or maybe I have that reversed? I have always done all three at the same time anyway.

Your viscosity sounds fine but I am not expert in that area. I have heard/read very good things about Valvoline products as an excellent substitute for Mopar, and it is what was used on my truck just yesterday.

Look for Valvoline Maxlife, and verify the limited-slip additive for the rear if you have that feature. You can still use it in any diff that doesn't have limited-slip so no harm if not needed.

 

[knightjp]

Thanks @Curmudgeon for the reply.
My truck calls for Synthetic Fluid and it seems that the Valvoline gear oil we get here is mineral.
I checked online and it does say to change ever 30k or even 15k - 20k if one does some serious off road travel or towing.
Transfer case is at 60k as well as the gearbox.

I've looked in the market and we have 75W-90 from Liquimoly.
Of course first preference would be to go for the stock Mopar fluid.

 

[Curmudgeon]

Yeah I thought all the lubes were supposed to be synthetic as the Mopar is, and I would not want to use conventional lube either.

It's been right around 30k since mine was done so yesterday I had both diffs and the transfer case serviced, in addition to draining out the Red Line 5-w30 and trying my 1st batch of HPL SC 0w-30 and same RP 20-820 filter.

 

[Wild one]

Thanks @Curmudgeon for the reply.
My truck calls for Synthetic Fluid and it seems that the Valvoline gear oil we get here is mineral.
I checked online and it does say to change ever 30k or even 15k - 20k if one does some serious off road travel or towing.
Transfer case is at 60k as well as the gearbox.

I've looked in the market and we have 75W-90 from Liquimoly.
Of course first preference would be to go for the stock Mopar fluid.

With those ambient temperatures i'd use the "towing" spec for fluid change intervals

 

[HEMIMANN]

Personally, I never understood the 140 viscosity spec for the rear differential for a light duty truck. 140 is normally reserved for heavy duty that tows. Maybe someone will chime in that knows what Ram was up to way back when.

Anyway, yes you are in 50C 122F area, hot ambient for any machine element. Beyond what I said above, how do you use your truck? Do you drive empty all the time? Most of the time? If you load or tow, do you load/tow heavy or little? How often do you drive in 50C 122F?

These answers determine how to spec viscosity. In terms of brands, past study data presented here showed Amsoil #1 and Mobil 1 #2 in performance test metrics. Personally I use Mobil Delvac 1 75W-90, as it has no limited slip friction modifier additive (one of the few that doesn't) because I have the AAM TracRite Torsen all gear differential that has no clutch packs. This auto-locking differential doesn't like friction modifiers - it delays locking.

 

[Wild one]

Personally, I never understood the 140 viscosity spec for the rear differential for a light duty truck. 140 is normally reserved for heavy duty that tows. Maybe someone will chime in that knows what Ram was up to way back when.

Anyway, yes you are in 50C 122F area, hot ambient for any machine element. Beyond what I said above, how do you use your truck? Do you drive empty all the time? Most of the time? If you load or tow, do you load/tow heavy or little? How often do you drive in 50C 122F?

These answers determine how to spec viscosity. In terms of brands, past study data presented here showed Amsoil #1 and Mobil 1 #2 in performance test metrics. Personally I use Mobil Delvac 1 75W-90, as it has no limited slip friction modifier additive (one of the few that doesn't) because I have the AAM TracRite Torsen all gear differential that has no clutch packs. This auto-locking differential doesn't like friction modifiers - it delays locking.

I don't remember any 1/2 tons that actually called for a 90 weight in the rear diff back in the day.It's only in recent years have they started calling for lighter fluids,and you can be dammed sure they aren't calling for lighter fluids for longevity. I'm guessing light duty trucks with a lighter duty rear end,put more stress on the fluid then a heavy duty truck with a heavy duty rear end does.Smaller ring and pinions/bearings etc,probably stress the fluid a bit more by creating more heat when under load,and don't have the surface area to get rid of that heat

 

[HEMIMANN]

Thanks, Rick, for validating I'm not quite ready for the old folk's home just yet.

btw, @knightjp if you drive distances or loads during the heat of day, I highly recommended Banks Cool Cover differential axle cover. I put one on my 2500 cause I tow moderate in 35C 94F ambient.

 

[crackerjack1957]

OP has a 1500.....Banks only makes for the 2500

Because of your high temps I would go with the 75W-140 in both differentials.
Have in both of mine recommended by East Coast Gear Supply after .456 upgrade.

 

[dieselscout80]

The OM for my 2020 Ram 2500 specs 75W-85 and the HDs trucks have NO bearing whatsoever on fuel economy standards as they aren’t even rated for MPG.

 

[HEMIMANN]

@Wild one btw, would the gear set size be proportional to the load such that the smaller 1500 axle would not get hotter than the larger 2500 axle? The 1500 truck is 1,000 lbs lighter than a 2500 and can only carry 1/4 the load.

Or is the load margin so much higher in the 2500 gears that it runs that much cooler when used unloaded most of the time?

 

[Wild one]

@Wild one btw, would the gear set size be proportional to the load such that the smaller 1500 axle would not get hotter than the larger 2500 axle? The 1500 truck is 1,000 lbs lighter than a 2500 and can only carry 1/4 the load.

Or is the load margin so much higher in the 2500 gears that it runs that much cooler when used unloaded most of the time?

I've always looked at it as there's alot more metal in a heavy duty diff to radiate the heat,and alot more surface area to spread the load out over,so you don't need as thick of fluid to provide the cushion needed

 

[crackerjack1957]

ecgs-gear-oil-recommendation1.pdf https://share.google/5mgqVcjLixU4GtPQU

 

[Hemi395]

In your climate, I would go with 75w140. Also, you would want to change your fluid more often, I would personally drain it at 20000 mile intervals. Obviously if it drains out clear you can then try 30 or 40k.

As for brand, it really depends on what you have available. Valvoline would be my first choice for an off the shelf gear oil. Plus they have the squeeze bags like Amsoil does, makes filling the diff so much easier. Ultimately though, I would recommend Amsoil Severe Gear if you can get it.

 

[DILLIGAF]

Amsoil Severe Gear 75W-140

 

[HEMIMANN]

ecgs-gear-oil-recommendation1.pdf https://share.google/5mgqVcjLixU4GtPQU

That looks like Lucas promotional quackery to me. Well reknown for such.

Here's my HD AAM axle - synthetics recommended, as are for GM axles.
dieselhub.com/axle/aam-11.5.html

 

[Wild one]

ecgs-gear-oil-recommendation1.pdf https://share.google/5mgqVcjLixU4GtPQU

That's a good read as long as you bypass their advertising for Lucas. I'm not a huge fan of synthetic diff fluids,i've had more bearings and ring/pinions go south with synthetic,then i have with the good ole cheap mineral gear lube. I ran mineral in my truck with the TruTrac,and it never had any issues,that's after going through 2 diffs using synthetic fluid.
I know synthetics get mighty thin when hot,as i always drain my diffs hot,and synthetic that's hot,drains like water compared to a mineral based lube that's hot

 

[crackerjack1957]

That looks like Lucas promotional quackery to me. Well reknown for such.

Here's my HD AAM axle - synthetics recommended, as are for GM axles.
dieselhub.com/axle/aam-11.5.html

You say so.......I have there gears & lube.....no issues but I change out lube every 10K.

Notice Lucas synthetic was not mentioned nor did they say the Lucas mineral gear oil was better than Amsoil or Redline.

Don't know of any professional gear shops that break-in gears with synthetic.

OEM factory differential assemblies.... the gears are broken in during factory testing with mineral gear oil
Synthetic is added after break-in

 

[HEMIMANN]

https://www.eaton.com/content/dam/eaton/products/transmissions/lubricants/synthetic-axle-lubricants/eaton-fe-75w-90-gear-oil-tcsl0023-en.pdf

GM does. At least on the HD diffs. I had one in the Kodiak 5500.

 

[Wild one]

https://www.eaton.com/content/dam/eaton/products/transmissions/lubricants/synthetic-axle-lubricants/eaton-fe-75w-90-gear-oil-tcsl0023-en.pdf

GM does. At least on the HD diffs. I had one in the Kodiak 5500.

Eaton also reconmends mineral based lube if you're using their trutrac limited slip.
I highly doubt what you're using is as important as changing it in a timely manner is.If you like to stretch your diff services out to 75,000+ miles,then you might want to use synthetic,but if you're changing your diff fluids at 30,000 or less miles,then i doubt a synthetic will show any advantage over a mineral based lube,except in how much more it lightens your wallet