This may be like asking "which is the best brand of oil" but I need opinions. I'm due to change the differential gear lube in my 2005 Dodge 2500. Last time I used Mobil 1 synthetic 75W-90. I should have gone with the 75W-140 since I'm towing but everything has worked fine so far.I am going to go with the heavier weight this time and am thinking about adding a PML aluminum finned cover to help lower the temps. It also increases the capacity .75 quart.I see a lot of folks on the Dodge forums using Amsoil and Royal Purple gear lubes. I'm wondering if the Mobile 1 is just as good. Any comments appreciated.

I think any of those oils will serve you well but when it comes to the cover, HERE is a screaming deal on the exact part Dodge and AAM use on the latest HO Cummins equipped differentials. It was designed by the manufacturer of the diff to lower temps and not so much just to be pretty.it's $400 at the dealer but this guy sell them for a great price (I bought one).

I has the same dilemma. I used 75w90 synthetic, and the ring gear area of the rear diff cover would have the paint burnt off it at the end of towing season. I added a huge aluminium rear diff cover and then filled it with Amsoil 75w110 synthetic - which for me was best. I worried about 75w140 being too viscous at low temperatures, like our -40* Canadian winters.BEFORE:AFTER:Note the puddle visible here is just water.

That's a good deal!Lube wise, just use your favorite flavor that is compatible with the limited slip.My 07, changed out the OE to Amsoil at about 20k mi both axles. Changed it again at 100k. Now at 120k and the posi still works like new. In fact the last oil change did not look much worse than the new oil. Didn't even change out the front axle, still like new.

Mine has Mopar 75w-90 in it @ $30qt and no sign of heat issues. I bet Wally's Super Tech 75W-140 Synthetic Gear Oil @ $11.37qt. is just as good.

Amsoil is the best in pretty much every catagory.RP pretty much sucks.Mobil is a very good lube for the price, but not the best.Here is some good reading for you. This will tell you how they ranked.

Differential gear lube. | Good Sam Community

ScottG
Nomad
Sep 16, 2013
I think any of those oils will serve you well but when it comes to the cover, HERE is a screaming deal on the exact part Dodge and AAM use on the latest HO Cummins equipped differentials. It was designed by the manufacturer of the diff to lower temps and not so much just to be pretty.
it's $400 at the dealer but this guy sell them for a great price (I bought one).
ib516
Explorer II
Sep 16, 2013
I has the same dilemma. I used 75w90 synthetic, and the ring gear area of the rear diff cover would have the paint burnt off it at the end of towing season. I added a huge aluminium rear diff cover and then filled it with Amsoil 75w110 synthetic - which for me was best. I worried about 75w140 being too viscous at low temperatures, like our -40* Canadian winters.

BEFORE:

AFTER:

Note the puddle visible here is just water.
Grit_dog
Navigator
Sep 16, 2013
That's a good deal!
Lube wise, just use your favorite flavor that is compatible with the limited slip.
My 07, changed out the OE to Amsoil at about 20k mi both axles. Changed it again at 100k. Now at 120k and the posi still works like new. In fact the last oil change did not look much worse than the new oil. Didn't even change out the front axle, still like new.
coolbreeze01
Explorer
Sep 16, 2013
Mine has Mopar 75w-90 in it @ $30qt and no sign of heat issues. I bet Wally's Super Tech 75W-140 Synthetic Gear Oil @ $11.37qt. is just as good.
Turtle_n_Peeps
Explorer
Sep 16, 2013
Amsoil is the best in pretty much every catagory.

RP pretty much sucks.

Mobil is a very good lube for the price, but not the best.

Here is some good reading for you. This will tell you how they ranked.
Turtle_n_Peeps
Explorer
Sep 16, 2013
Turtle n Peeps wrote:
Amsoil is the best in pretty much every catagory.

RP pretty much sucks.

Mobil is a very good lube for the price, but not the best.

Here is some good reading for you. This will tell you how they ranked.

Oh, BTW; I would not go 140; but your gears and your money. :)
dryfly
Explorer
Sep 16, 2013
ib516 wrote:
I has the same dilemma. I used 75w90 synthetic, and the ring gear area of the rear diff cover would have the paint burnt off it at the end of towing season. I added a huge aluminium rear diff cover and then filled it with Amsoil 75w110 synthetic - which for me was best. I worried about 75w140 being too viscous at low temperatures, like our -40* Canadian winters.

BEFORE:

AFTER:

Note the puddle visible here is just water.

Well, I'm a little concerned about the 75-140 here in the Texas heat! I'm thinking the 75w110 might be fine assuming I go with Amsoil. There are a lot of folks over on the TDR Dodge forums using Amsoil.
bgum
Explorer
Sep 16, 2013
Amsoil is highly rated by Amsoil.
mrekim
Explorer
Sep 16, 2013
I would look for "meets" or "exceeds" either or both of these specs:

MIL-PRF-2105E

SAE J2360

As an example:

Valvoline/Full synthetic gear oil SAE 75W-140

was the first one I found in a search...
DUNEBUGGYDOUG
Explorer
Sep 16, 2013
Your ring and pinion gears do not really care what brand is used as long as they are lubricated