Downside to 75-140 vs 75-90 in my Ram 3500

[cronk]

When I started towing with my 93 Chevy 1500, I switched to Valvoline 75w140 synthetic. No measurable loss in mpg.
For your application, I think a 75w140 would be fine.
Often manufacturers recommend the lighter gear oil to bump up their CAFE "corporate average fuel economy", though in real world conditions the difference is negligible.

 

[deeter16317]

Originally Posted By: cronk

Often manufacturers recommend the lighter gear oil to bump up their CAFE "corporate average fuel economy", though in real world conditions the difference is negligible.




While this applies to a 1500, the 2500 and 3500 series trucks are typically exempt from CAFE numbers since they are considered to be more of a "commercial" application (for lack of a better term).

 

[deeter16317]

Just a follow-up...I drained my RP 85w140 today, there was almost no fuzz on my rare-earth magnet (super strong pull), and the fluid looked as good as the day I put it in (it was still purple). The funny part is that fluid was changed last at 80735, and the truck currently sits with 212820. I'm filling with Schaeffers #167 75w140 full synthetic, and don't plan to touch it for at least another 100k.

 

[bullwinkle]

Originally Posted By: bmwtechguy
I think you made a good decision that was biased towards durability (vs fuel economy) with the 75W-140 since you are pulling a horse trailer and have a limited slip. Clutch-based limited slip diffs tend to run hotter than open diffs.
Pretty sure that the newer Rams have a helical gear type locking rear differential-no posi lube needed. That said, I ran Longrider/RP 85W140 full synthetic in my 2002 Ram 2500 Dana 80 w/no posi lube, worked fine! Royal Purple states that their gear oil has the posi additive already in it.

 

[deeter16317]

Dodge uses a type of gear LSD (trac-rite, not to be confused with the Dana trac-loc) in the 11.50AAM...it still uses clutches termed "shoes" in the FSM. Basically the gears push the "shoes" into the housing...the more power input (assuming equal traction under both wheels), the harder they are applied. Some owners still report chatter, and the fix has been to add some LSD modifier just like you do with the plate type LSDs.

Its my understanding that GM uses a form of the G80 gov-loc in their 11.50AAM, which is a full-locking plate-type LSD. A few Dodge owners have successfully transplanted this LSD into their trucks because they can be had for cheap oftentimes.

 

[dave123]

What was used and final weight used do we know???