I have to second that.

 

Good thinking....do it yourself. You know what I mean

 

I'm on here tonight because my newly received Mag-Hytek covers recommended GL5-MT-1 LE 992 75-140 GL5 Synthetic. This for a 2005 Ram 3500 4x4 with 9.25 F and 11.5 R AA axles. Haven't yet picked the brand to put in. They do hold a LOT more oil though.

 

The rear cover has been on my truck for approx. 7000 miles now with 75/140 Valvoline full synthetic in it.... I tow heavy loads in the Texas heat around here.. its not just the heat for the differential, its the CONSTANT loading and unloading of the ring and pinion due to all the hills. We don't really have the long constant hills like mountanious regions have. Its those 1/4 to 1/2 mile "up one side and down the other" over and over. Same for the engine, the turbo is constantly loading and unloading.
Haven't seen any fuel mileage drop from the 75/140... and I KNOW the differential is living a healthier life with the added oil capacity and cooling fins. I heard Mrs. Claus was on the phone with Geno's the other day making sure that my sled gets some front differential "bling" for Christmas!!!

 

The 75-90 is what is recommended and I would ALWAYS pick synthetic over dino.

I switched to Mobil 1 75-140 when my diff startd the chattering thing. It was fine for over 100,000 miles with the 90 but then when hot and starting out while towing or loaded, with front wheels turned, it started the chatter. Seems like the 140 has fixed it and I haven't seen a mileage drop. It had been changed several times and always filled with the Dodge stuff. So I've concluded that the limited slip action is probably not as aggressive with the higher viscosity oil.

Probably best to go with the 90 unless you have reason not to. I'm amazed how much use and abuse these axles can put up with!

John

 

X3....that is tooooo **** funny.

jim

 

Oh, but you'll put stuff in your own rear end?

 

I changed over to the 75/140 Mobil1 this last change and I have not seen any negative effects. I tow about 5% of the time, but no appreciable change in MPGs regardless. An aftermarket cover would have been nice to install - maybe next time!