diff fluid change on a 3.21

[ramffml]

So I've been looking into changing the diff fluid on my truck, 5th gen with 3.21.

Amsoil apparently does not make a product for it? On the webpage there is nothing listed for the 3.21. They do for the 3.92, but they apparently recommend using mopar/oem fluid for a 3.21.

The manual calls for:
3.21: 75W-90 with additional friction modifiers for limited slip
3.92: 75w-140 with additional FM for LS
3.92 max tow: Dana SAE 80W90

Can/should I be running amsoil 75w-110 in my 3.21? Or should I follow amsoil's advice and run mopar fluid.

I tow quite often, 5000 to 6000 pounds these days.

 

[danielmid]

I'll stick with my recommendation of 75w-140, Red Line or Amsoil. 140 will handle the towing heat better than the 90 and the 110. Here's screenshots from Red Line's website.

 

[ramffml]

I put thicker engine oil in my truck so I get the heat thing, but just concerned about the viscosity and clearances etc in the diff. Hopefully the reason amsoil is not recommending it is simply because they're "following the spec down to the last letter" rather than being some real world issue with running the thicker oil.

Because that 3.92 vs 3.92 max tow is a head scratcher, they recommend a much thinner oil there in the max tow, most likely a different axle altogether?

 

[turkeybird56]

So I've been looking into changing the diff fluid on my truck, 5th gen with 3.21.

Amsoil apparently does not make a product for it? On the webpage there is nothing listed for the 3.21. They do for the 3.92, but they apparently recommend using mopar/oem fluid for a 3.21.

The manual calls for:
3.21: 75W-90 with additional friction modifiers for limited slip
3.92: 75w-140 with additional FM for LS
3.92 max tow: Dana SAE 80W90

Can/should I be running amsoil 75w-110 in my 3.21? Or should I follow amsoil's advice and run mopar fluid.

I tow quite often, 5000 to 6000 pounds these days.

following, since I have a 3:21 in MY 19.

 

[danielmid]

I put thicker engine oil in my truck so I get the heat thing, but just concerned about the viscosity and clearances etc in the diff. Hopefully the reason amsoil is not recommending it is simply because they're "following the spec down to the last letter" rather than being some real world issue with running the thicker oil.

Because that 3.92 vs 3.92 max tow is a head scratcher, they recommend a much thinner oil there in the max tow, most likely a different axle altogether?

It's weird because Red Line recommends similar, why would they want thinner oil on the higher tow rated config? It doesn't make sense to me. I'm going to lean on the usual answer and say it's thinner at operating temps which will eek out some small % increase in fuel economy, but again the max towing spec is throwing me off.

For me, I'll stick with the thicker oil at high temp that will protect better.

 

[Wild one]

The 1500's don't have a Dana rear axle,no matter what tow rating rating,i'm guessing that must apply to an older heavy duty truck.
My wifes Challenger has the famous ZF howl,and switching it from the reconmended 75W-90 to 75W-140 Redline made a hell'va differance in the noise coming out of the rear diff.
If it was my truck i'd run 75W-140,as that's what they used to reconmend up till i think somewhere around 17 or 18,and they're ZF diffs

 

[Wild one]

I just went through my 700 page printed manual for my 14,and nowhere do they say anything about a 3.92 "max tow rating", all they say is to use 75W-140 and add friction modifier if you have the limited slip diff

 

[ramffml]

I just went through my 700 page printed manual for my 14,and nowhere do they say anything about a 3.92 "max tow rating", all they say is to use 75W-140 and add friction modifier if you have the limited slip diff

Looks like a 5th gen thing. Only seen a couple posts on this so far on the other ram (5th gen) forum, one post said it's dana 60 super axle and a different post said they just use a bigger gear.

This is the screenshot from my manual, the reference to "dana" lubricant:

 

[Wild one]

Looks like a 5th gen thing. Only seen a couple posts on this so far on the other ram (5th gen) forum, one post said it's dana 60 super axle and a different post said they just use a bigger gear.

This is the screenshot from my manual, the reference to "dana" lubricant:

Does your manual say anything about the 2500's and heavier trucks.I wonder if maybe they're referring to the heavier trucks,as my manual does list the 2500 and up as using 75W-90,and it's seperate from the 1500's

 

[ramffml]

Does your manual say anything about the 2500's and heavier trucks.I wonder if maybe they're referring to the heavier trucks,as my manual does list the 2500 and up as using 75W-90,and it's seperate from the 1500's

At the top of the very first page it just says "The all-new ram 1500 user guide", and a keyword search for "2500" shows 0 results.

I think the max tow is one of those unicorns/special orders, 4x2 + single cab etc. There is a tow package option which includes tow mirrors + 3.92 + one or two other things but think that's still different than the "max tow".

 

[ramffml]

Found a copy of the 2023 5th gen, still shows the same section. If you open the pdf and search for "dana" you'll jump to the relevant section.

But just checked the build and price tool, doesn't show it anywhere. Bizarre.

https://cdn.dealereprocess.org/cdn/servicemanuals/ram/2023-1500.pdf

 

[Wild one]

Found a copy of the 2023 5th gen, still shows the same section. If you open the pdf and search for "dana" you'll jump to the relevant section.

But just checked the build and price tool, doesn't show it anywhere. Bizarre.

https://cdn.dealereprocess.org/cdn/servicemanuals/ram/2023-1500.pdf

It really doesn't say much about the max tow rated diff does it,other then the fluid viscosity

 

[crash68]

If all your truck is a daily driver, the 75W-90 is fine for the front and rear. If your working the truck at all go with 75W-140 in the rear.
As a side note, a Dodge dealership mechanic told me all the differential services they did were with 75W-90 Mobil 1, he said it didn't matter if it was a 1500, 2500 or 3500.

 

[Wild one]

Everytime they go after milege number increases,all the fluids seem to get lighter. I don't know how well that'll work out in the long run,if you like to keep your vehicles for a long time,and mile them out.
Look at what they're reconmending for oil in the 5.7 now, 0W-20,i've never seen anywhere that says 0W-20 is good for longevity,all i've ever seen them say is it's better for cold weather starting and milege,and i think if it added to the longevity of the engine,they'd be bragging it up

 

[ramffml]

My issue with the 140 is not the idea that thicker oil is better protection, I get that no problem. My issue is that going from 5w-20 to a 5w-30 seems like a tiny step in comparison to going from a 75w-90 to a 75w-140, that appears to me to be a very large jump in viscosity. That would feel like me going to a 5w-50 in engine oil or whatever... there comes a point when going thick is now too thick, right? Just want to make sure the 75w-140 isn't going to cause issues.

I know, my feelings just run me don't they?

I appreciate you all helping me out!

 

[Wild one]

My issue with the 140 is not the idea that thicker oil is better protection, I get that no problem. My issue is that going from 5w-20 to a 5w-30 seems like a tiny step in comparison to going from a 75w-90 to a 75w-140, that appears to me to be a very large jump in viscosity. That would feel like me going to a 5w-50 in engine oil or whatever... there comes a point when going thick is now too thick, right? Just want to make sure the 75w-140 isn't going to cause issues.

I know, my feelings just run me don't they?

I appreciate you all helping me out!

I wouldn't worry about it,as it operates very similiar to 90 or 110 until the diff gets hot.Remember up till about 2017 they called for 140 in the ZF diffs,then milege numbers became a factor,and fluids started to get lighter.I haven't found anybody including Ma Mopar that says the lighter fluid is good for longevity,and i'd hazard a guess if it was better for longevity,they'd be bragging it up

 

[JHoward]

I wouldn't worry about it,as it operates very similiar to 90 or 110 until the diff gets hot.Remember up till about 2017 they called for 140 in the ZF diffs,then milege numbers became a factor,and fluids started to get lighter.I haven't found anybody including Ma Mopar that says the lighter fluid is good for longevity,and i'd hazard a guess if it was better for longevity,they'd be bragging it up

Yep, exactly ...

 

[JHoward]

My issue with the 140 is not the idea that thicker oil is better protection, I get that no problem. My issue is that going from 5w-20 to a 5w-30 seems like a tiny step in comparison to going from a 75w-90 to a 75w-140, that appears to me to be a very large jump in viscosity. That would feel like me going to a 5w-50 in engine oil or whatever... there comes a point when going thick is now too thick, right? Just want to make sure the 75w-140 isn't going to cause issues.

I know, my feelings just run me don't they?

I appreciate you all helping me out!

Well, remember. They spected 5w/30 for the HEMI when it debuted back in~2002 and gradually went to "thinner oil" to meet the "EPA fuel economy standard(s)" with no regards to longevity of an HEMI engine. If you get longevity, then good and if not, oh well.

Then that beautiful invention, VVT/MDS combo, came on the scene~2008 moving the cam higher in the engine block making the already poor oiling design worse and spec 0w/water oil to meet the recommended "tree huggers" fuel mileage/economy standards. Oh, boy.

I'm thinking about doing an differential oil change and I wouldn't be afraid to use an heavier oil because I want longevity and I'm not concerned about fuel economy ...hey, I have a truck.

If I want to save gas I'll ride my motor bike, without wearing the "leather clothing"... to help further save gas, lol.

 

[Wild one]

Well, remember. They spected 5w/30 for the HEMI when it debuted back in~2002 and gradually went to "thinner oil" to meet the "EPA fuel economy standard(s)" with no regards to longevity of an HEMI engine. If you get longevity, then good and if not, oh well.

Then that beautiful invention, VVT/MDS combo, came on the scene~2008 moving the cam higher in the engine block making the already poor oiling design worse and spec 0w/water oil to meet the recommended "tree huggers" fuel mileage/economy standards. Oh, boy.

I'm thinking about doing an differential oil change and I wouldn't be afraid to use an heavier oil because I want longevity and I'm not concerned about fuel economy ...hey, I have a truck.

If I want to save gas I'll ride my motor bike, without wearing the "leather clothing"... to help further save gas, lol.

Are you saying riding it naked would give you the best milege

 

[JHoward]

Are you saying riding it naked would give you the best milege

Well, my state has an mandatory helmet law .. so, at least I'd have to wear that ...