I don't wanna and you can't make me. :-P

All I know is, I used to run 140 in my ZJ. And at the time I lived in Utah and it would get down to 0-5 degrees outside and the axles wouldn't loosen up till I drove it 30+ miles. And when I would go down to AZ in the winter, I would get horrible gas mileage till I hit south of St. George,Ut. Now I run thinner gear oil till I know I'll be hauling something heavy enough to need 140.

 

(Let this be my occasional post)
Since it's hitting 100+F daily where I am now, let me tell you this: I become less excited as the temperature further exceeds 75.

 

OK...I changed out the gear lube, put 75-90 syn in it. Now when I turn - forward or reverse - I get a clicking, snapping noise. Do I need to add a lsd additive?

 

Hey! another Nord-Dakota'r!
Bismarck/Mandan here... good to see a local!
Cant answer your question, just saying hi!

I did put new fluids in both my front and rear dif and just used whatever 75W-90 the local autoparts place had in stock with no additive that I recall....

 

Just to point out. Today I drove my truck around the city. A good 1 hour of city driving 40mph tops and stop and go traffic and then towing my trailer just 1 block. And 100 degree weather. I used my Infrared Thermometer.

I got a high of 130 degrees and an average of 120 degrees around the housing and cover.

After 30mins of driving at 75 highway driving I got a high of 150 degrees, average 130 on the housing and cover.

 

That sounds reasonable and about what NorDak described: Too hot to holt, but not too hot to touch for a second. you are also turning larger tires than stock. That would create a bit more friction with the more mass, BUT would also make the axels turn slower, right? Might wash in the long run.