Dodge AAM gear lube weight??

[wilnis]

I have an 04 Dodge Cummins 2500 and the owners manual recommends 75-90 synthetic gear lube for front and rear differential (changing the lube every 15,000 miles). The Dodge Ram forums all talk about a TSB that recommends 75-140 synthetic for towing in the rear, but my buddy at a local 5-star has scoured the books and can't find alledged TSB, and if one calls AAM, they specifically recommend 75-90 synthetic. Several posters on Dodge forums point out that this is just a "recommendation" from Dodge and AAM, and with towing heavy (I tow 7000-10,000# regularly) one gets better protection with the higher weight lube.
My question, What do Bitogers suggest? Is the 75-90 product providing enough protection as AAM would have "certainly" tested for that in developing the differential, or am I getting better protection by increasing the weight to the 75-140 given my truck does lots of towing in summer with temps of 80-100 degrees?? I've talked to service managers at two different 5-Stars and gotten opposite recommendations!!

Thanks for the input. Bill

 

[racer12306]

a 75w90 synthetic gear oil should provide enough protection. my dad just changed the gear oil in his 05 2500 with 75w90 redline front and rear. he does not tow as much as others, actually now its pretty rare that the truck tows. since the manual and AAM say 75w90 you should be fine with that. but if you are concerned then you should be fine using 75w140.

in my personal opinion, as well as my dads. 15000 miles is way too often for changing the gear oil. the chevy has almost the same rear behind their HD trucks, except the axle tubes are smaller. chevy recommends a 100,000 mile change interval. but since you are under warrenty you may want to do it every 15000. my dad will probably not change his for a while.

 

[Jim Allen]

The consensus among the people I have consulted with, axle design engineers (Dana, Arvin Meritor and AAM) and oil makers, is that if your diff temp exceeds 200 degrees for significant periods, you should have a 140 wt. If you regularly tow 10,000 pounds, I guarantee you are running over 200 degrees a significant portion of the time. Also if you tow, the 15K OCI is not out of bounds with reality. Watch for the July issue (on stands in June) of Four Wheeler magazine for more info on the topic. It'll give you more info on ways to cool the overly hot rear end!

 

[racer12306]

thanks for a more technical insight on the subject. i was thinking it had to do with lots of towing and such as far as to use 75w90 or 75w140.

 

[bmwtechguy]

If you want best fuel economy, use a quality synthetic 75W-90, but if you run heavily loaded, often in hot weather, then I would go with the heavier 75W-140 synthetic as others have said, for better wear protection. 15k miles does seem a tad often to change out the diff oil. Why not sample a couple times to establish a safe interval and save yourself some $ in the long run. Seems like at least double that interval with Amsoil or Redline diff oils would be ok, but verify with oil analysis to be certain.

 

[1sttruck]

Dodge is funny about the change interval, but not funny 'ha ha'. It's 15k for severe service as noted, but none seems to be stated otherwise. I used 75w90 teh first time, Mobil 1, and it looked fine at the next 15k, where I switched to 75w140. The 75w140 is a lot more expensive, but it does seem to make for a bit less drivetrain noise, and I don't tow anything. I'll probably switch back to 75w90 in the front, and stay with 75w140 in the rear.

But then there is always mixing, where I could use .... :^)