75w90 vs 85w140?
 

Ok, I have spent numerous hours conducting due diligence on the best grade of t-case and diff oil to use in Washington State. The only thing consistent is that everyone recommends either weights/grades. Perhaps we can just just have one thread on here that addresses just this. One thing I was thinking of doing was using the LR recommended grade of 75w90 on the diffs and using the 85w140 in the transfer case .... any thoughts on this ... what do you use and why? Thank you. With Respect, LT

85w140 takes longer to heat up to temp= more resistance on drivetrain. Mixed that with diffs and an engine / trans that wants to turn faster and you'll be setting yourself up for a gradual thermal dynamic failure of the tcase.

I was advised to use the 85w140 since it was thicker and would protect better under the heat and strain. I ended up with Royal Purple 85w140 sythetic.

Where the hell did you come up with that crock of S--- explanation and be very specific.
When cold the viscosity of the 85/140 is 85, just as it should be and when hot it is 140 for the extra protection needed to protect our somewhat fragile spider gears.

That being said, disregard that reply and run only the higher viscosity gear oils be it dino or syntheic.

Thanks Disco, I trust anything you say. I'm going with the 85/140. Now I need to figure out what synthetic oil to use for Washington State, I think 10w30 was too light as new leaks starting popping up. Also, Is royal Purple the best brand for t-case and diff? Money is really not a factor. Thank you all!.

To me 15/40 is as light as I would go (unless you live in the eastern part of the state in winter), I use 20/50, just an old preference. The synthetic vs dino oil is an old one that has no answer, use what you feel comfortable with, personally I think the only advantage with synthetic is longer replacement intervals which I don't believe in. (I'm sure this last statement will raise all kinds of responses, it's kind of like asking which political party you belong to:D)

Crock of ****? Clearly you dont understand thermal dynamics. He asked if it was o k to run thicker gearoil in the tcase and lighter inin the diffs.
Clearly, you cant read, so my explanation of thermal dynamics would be completely lost on you.

I'm still have to change out my diff and TC oil and thinking of getting this from Amazon. Redline 75w-90 in a 5 gallon for $72.91 delivered.

I would still suggest you run the 85/140, especially up inn your warm area, but that is your call.

Amazon also has the Red Line 75w-140 for the same price.