Diff oil viscosity for heavy towing

[LRutigliano]

I searched the forums and can't get a definitive answer.



I use my truck for towing the 11k 5er 100% of the time. I mainly tow in the summer and tow up big grades up to 4000+ ft elevation. I have many modifications for increased engine power too.



I have front and rear PML diff covers and currently use Valvoline Syntech 75W-90 gear oil for both.



Every time I change the oil (seems like every 3k), I notice some metal flakes and the oil is darker than new.



Before the PML covers, my rear stock diff cover flaked the paint or undercoating or whatever was on it off big time, in big chunks.



I think I'm a good candidate for Amsoil 75W-140 or Valvoline 75W-140 for the diffs, but want to make sure its ok.



For those of you that tow: do you agree and should I change to the heavier oil in the rear AND the front?



Thanks,

Louis

 

[HOBrian]

Dodge does recomend the 75w 140 for heavy towing. I don't think you need to run it in the front though might be too heavy.

 

[DGamelin]

I cant find where dodge recommends 75w-140 but I would think it is a good idea if you live in the south (heat) . I live in the north my trucks run to TX and back with loads of around 15k and more on the 3500, no more then 12k on the old dog. Just change lubes I used 75-90 valvoline, trying to squeeze every mpg I can. The 3500 rear axle had more mentalis in it then a paint job. 2nd change in 50k miles. The 1st owner had amsoil put in it. I think ether brand is fine.



04. 5 3500 cc 4x4 drw 373 6speed 50k

93 2500 xc srw 2wd 354 auto 250k

 

[AH64ID]

Dodge does recomend the 75w 140 for heavy towing. I don't think you need to run it in the front though might be too heavy.

No they don't... .

The AAM 11. 5 has always had 75w-90 as the recommend viscosity, and it has been the axle for the most hp and highest tow ratings Dodge has ever had...

That being said there are many that use it without any issues... I would say that if you tow for most of your miles you will be fine... but if your empty for most your miles I would stay away from it, it will be harder on the gears once it gets warm...

Amsoil also makes a 75w-110 that splits the two, and IMHO is probably a good choice for the AAM. Personally I will stick with the 75w-90 that amsoil makes, with the good quality synthetic and the mag-hytec I am not worried... But if I lived with a trailer hooked up I may think about the 110 or 140.

 

[dan.poitras]

I've been using Amsoil 75w140 in front and rear since new with no issues and gets down to -30F at times in the winter.

 

[Gary - K7GLD]

Mine's a 2nd generation truck, with the Dana 80 differential, but I feel the same viewpoint applies. I tow a lot (RV), and usually in the mountains, so I use the same Ford synthetic 75/140 differential lube as they use in their similar Dana 80 differentials - no problems so far...

 

[HOBrian]

No they don't... .

IF you look back far enough there has been discussed the use of a 75w-140 gear oil. Some even had said that dodge does recommend the use of this oil if you are towing... and since this truck is towing 100% of the time, my original post still stands correct.

 

[DPKetchum]

None of the service manuals call for the 140wt. in the 2500/3500 AAM axels. The Corperate rear axel used in the 1500s call for the 140wt. Paint falls off all the differantial covers.

 

[TAbbott]

Gary - K7GLD said:



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Boy Howdy!! You nailed it there Gary! Maybe that'll be the wake up call we need to vote all of those idiots out of office; start drilling; refining; and building new nuclear power plants, etc. so we might actually become energy independent.

 

[AH64ID]

IF you look back far enough there has been discussed the use of a 75w-140 gear oil. Some even had said that dodge does recommend the use of this oil if you are towing... and since this truck is towing 100% of the time, my original post still stands correct.

Look back how far, the current axles are only 5 model years old... I have never need it discussed for the AAM axles... Show me something that says AAM/Dodge says to use more than a 75w-90...



and like I said in my post, towing ALL the time a 140 would probably be okay... but you have to be towing ALL the time.

 

[BHolm]

That being said there are many that use it without any issues... I would say that if you tow for most of your miles you will be fine... but if your empty for most your miles I would stay away from it, it will be harder on the gears until it gets warm...



.

I think you are wrong on your assertion that 75-140 will be harder on gears until the oil warms up. Both 75-90 and 75-140 are designed to flow like a 75w when cold, hence the 75w designation. The 140 version obviously has some additives to extend its ability to protect at higher temps but that does not mean it doesn't flow well cold.



If you can back that up with cold pour statistics I will listen, but it seems off-base to me.



I ran several trucks with the Amsoil 75-90 in front and 75-140 in back. Some towed all the time, some did not. All were exposed to extreme cold and hot temps at times, none ever gave me any trouble. Unless you tow in 4x4, I don't see any need for the 140 up front. My front diffs always drained as clean as the day it went in and rears were always dark with some metal. I've never had a truck that didn't do that so I think it is pretty much normal.



With increased capcity and extra cooling from upgraded covers I would think you would be fine with 75-90. The 11k lb trailer still leaves you several thousand pounds shy of the trucks rated capacity. I have run them over rated capacity for 100k miles, stock diff covers, 75-140 and a 50k change interval, no problem. My F350, used the same, with a Sterling 11. 5 (or 11. 0 don't recall exactly) needed an axle rebuild at 100k running the Ford 75-140 fluid. I think the AAMs are pretty tough.

 

[LRutigliano]

I think you are wrong on your assertion that 75-140 will be harder on gears until the oil warms up. Both 75-90 and 75-140 are designed to flow like a 75w when cold, hence the 75w designation. The 140 version obviously has some additives to extend its ability to protect at higher temps but that does not mean it doesn't flow well cold.



If you can back that up with cold pour statistics I will listen, but it seems off-base to me.



I ran several trucks with the Amsoil 75-90 in front and 75-140 in back. Some towed all the time, some did not. All were exposed to extreme cold and hot temps at times, none ever gave me any trouble. Unless you tow in 4x4, I don't see any need for the 140 up front. My front diffs always drained as clean as the day it went in and rears were always dark with some metal. I've never had a truck that didn't do that so I think it is pretty much normal.



With increased capcity and extra cooling from upgraded covers I would think you would be fine with 75-90. The 11k lb trailer still leaves you several thousand pounds shy of the trucks rated capacity. I have run them over rated capacity for 100k miles, stock diff covers, 75-140 and a 50k change interval, no problem. My F350, used the same, with a Sterling 11. 5 (or 11. 0 don't recall exactly) needed an axle rebuild at 100k running the Ford 75-140 fluid. I think the AAMs are pretty tough.

BHolm,



Thanks for the info! And also thanks to all for posting.



I will probably go to the Amsoil 75W-90 when I change it next. I've read the test report that Amsoil published and their oil sure seems much better than all others.



I checked the Valvoline oil on FRI in the rear diff and it was still golden color after 2000 miles. However, I spray painted the pumpkin when I installed the PML cover 2000 miles ago and the paint is starting to flake off. I'm not sure if its due to heat or the non-prep work I did.

 

[AH64ID]

I think you are wrong on your assertion that 75-140 will be harder on gears until the oil warms up. Both 75-90 and 75-140 are designed to flow like a 75w when cold, hence the 75w designation. The 140 version obviously has some additives to extend its ability to protect at higher temps but that does not mean it doesn't flow well cold.



If you can back that up with cold pour statistics I will listen, but it seems off-base to me.



I ran several trucks with the Amsoil 75-90 in front and 75-140 in back. Some towed all the time, some did not. All were exposed to extreme cold and hot temps at times, none ever gave me any trouble. Unless you tow in 4x4, I don't see any need for the 140 up front. My front diffs always drained as clean as the day it went in and rears were always dark with some metal. I've never had a truck that didn't do that so I think it is pretty much normal.



With increased capcity and extra cooling from upgraded covers I would think you would be fine with 75-90. The 11k lb trailer still leaves you several thousand pounds shy of the trucks rated capacity. I have run them over rated capacity for 100k miles, stock diff covers, 75-140 and a 50k change interval, no problem. My F350, used the same, with a Sterling 11. 5 (or 11. 0 don't recall exactly) needed an axle rebuild at 100k running the Ford 75-140 fluid. I think the AAMs are pretty tough.

Yeah I said that backwords... thanks for catching it...

 

[JHardwick]

I've ran Mobile1 75w-90 in the front, and 75w-140 in the rear for 403,991 towing miles as of this posting.

I've tried a couple other brands and always pick up a chatter on a hard turn.

 

[AH64ID]

I've tried a couple other brands and always pick up a chatter on a hard turn.

Thats very odd as the LSD used in the AAM is not clutch driven and wont chatter...

 

[DPKetchum]

I use the Amsoil Severe Gear 75w90 and picked up SEVERE chatter on left turns and starting off pulling 10k after differential got hot. I then searched ARCHIVES on several different Dodge forums. Found a few threads describing same issue. Found some discussion on the Carson Dodge forum. Long and short of it I bought a generic anitchatter additive at Auto Zone. Poured it in. 10 miles latter NO chatter. AAM said that shouldn't happen. Amsoil said "don't know but we do say might need additive". But I did find other posts stating just about the same situation mine did in and thats what fixed them. Anti Chatter additive.

 

[AH64ID]

Very weird... yeah by design a helical gear LSD shouldn't chatter, even a friction modifier wouldn't do anything as there are no clutch packs.

 

[steved]

The cure for the chatter is LSD additive; yes, even in the AAM axles.



There were threads about the use of 75w140... it was in a memo, by dodge, to its service writers IIRC. It was intended for those that are either loaded heavy or tow often.



With that said, I guess my rear diff is going to blow up since I use 85w140 Royal Purple... I too suffered the "burnt" 75w90 and paint falling off the cover... I actually gained MPG upping to 85w140 and the diff runs much cooler (even before adding the aluminum cover).



IMHO, the use of 75w90 is really for fuel mileage only, not protection of the differential...

 

[JHardwick]

Our AAM does in fact have clutches.

 

[steved]

Our AAM does in fact have clutches.

Yes, they are termed "shoes" in the drawings...