Engine/Transmission (1998.5 - 2002) 75w90 or 85w140 in rear diff?

[Hohn]

The heavier lube won't hurt anything at all. But, like others have said, you probably won't need it.



I've run Mob 1 75W-90 and it seemed fine. Now i run Redline ShockProof Heavy-- which is basically a reddish-purple lube as thick as vaseline. But it works VERy well. On the Bobistheoilguy site, he commented how the Redline shockproof sticks to gears almost like it's paint! No dry starts. Not to mention the superior High-Temp protection of the Redline oils.



If you use a premium synth gear oil- (amsoil, RP, Redline, Neo, etc), I would say a 75-90 should be more than enough under ANY circumstances. make sure it's a well-regarded synth gear oil though, not just some autoparts store oil du jour.



If you want to never worry about it, run the heavier stuff in a high-quality lube. Redline shockproof heavy is about the toughest lube you can buy. I haven't noticed any lower mpg or negative effects (diff noise, etc) since I switched.



Justin

 

[Gary - K7GLD]

One basic issue that has plagued use of the Cummins right from the very begining in our trucks, has been the extreme low end torque combined with combustion firing impulses spaced significantly farther apart than other engine types. This produces what some have edescribed as a "jackhammer" effect on drivetrain components, and is likely responsible for many, if not MOST manual transmission failures - the early manuals behind the Cummins would just plain peel the gear teeth off. After addition of the overdrive units on the automatics, lockup clutches just simply couldn't hold the power impulses, and failed at an alarming rate - sure helped DTT and ATS's buisiness tho'!



Those SAME widely-spaced impulses ALSO eventually work their way back to the differential, and unless lube providing superior shear and load strength are used, potential damage exists...



I personally see NO reason to gamble - I recognize DC's recommendation of heavier lube in towing situations - it costs no more, and seems like a no-brainer to not follow their advice...

 

[rblomquist]

Originally posted by Gary - KJ6Q

I personally see NO reason to gamble - I recognize DC's recommendation of heavier lube in towing situations - it costs no more, and seems like a no-brainer to not follow their advice...

That's what I keep going back to myself.

 

[Cooker]

Certainly we don't believe everything DC says, nor follow all of their recommendations. To each his own.

 

[Gary - K7GLD]

"Certainly we don't believe everything DC says, nor follow all of their recommendations. To each his own. "



YUP - I'd sure hate to lose the fun of all the non-DC approved stuff I have on MY truck!

 

[RobertMiller1]

The heavier lube won't hurt anything at all.

It does hurt fuel mileage.

the heavier diff fluid, has more effect than you might realize. 1 - 2 mpg.

Best of both worlds might be the Redline Shockproof lighweight. 75w90.

A high mileage CTD/ram might run 10w30 syn engine oil, and 75w90 redline in differentials



but, I am a big bore fan too... so it's 15w40 oil and 85w140 differential oil for me...



I personally run valvoline 85w140 semi as I have it in my trail rig/crawler/mudder. (also a diesel)



86DieselTrooper