Differential Fluid Weights

[Bersaglieri]

I'm due for a differential fluid swap so I asked few local guys what they've been using. I heard pretty much what I expected to hear..."Whatever the manual says" and "75w140 if you tow, 80w90 if you don't". Really there is not definite line on where to consider the heavier weight fluid...

Here is my issue, I tow occasionally, sometimes it's 3 tons of gravel in the bed of the truck, other times it's a 22ft lowboy gooseneck with a car or truck on it. I may only tow 3-4 times a month, but, I live in southern New Mexico and summer is upon us. It's going to hang in the 95-110 degree temperature range for the next 6 months. So, with the ambient temperature in mind and some occasional towing, what do you guys think I should run?

PS: Is synthetic worth the money? I can get a gallon of dino for $14 or a quart of synthetic for $11.

-Dustin-

 

[Diehard Ram]

I run synthetic gear lube in all my stuff. I see a difference in using it. I use 75w90 in my stuff. I have used synthetic for a long time now, and i will never go back to non synthetic.

 

[1-5-3-6-2-4]

75w-140 synthetic for sure in the Rear diff.

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[breakin point]

I use 75-140 royal purple synthetic in my diff. and I have seen a difference in the oil temp while towing