I do oil sampling on all fluids that I change out, the tests on the front/rear diff fluids come back with almost similar information, little less visconsity in the rear fluids but not that much different. I am running Amsoil synthetics in all my drivetrain components.

I think that the much hotter road temps here in the southwest warrant more frequent changes and addition of a little more capacity of fluids has proven to be good as well.

I also have the Fast Coolers on my tranny, the temp change with the finned aluminum and added capacity reduced my tranny temp by 50*s. The temp change on my front diff was 35*s reduction after adding the MH cover. The temp change on my rear diff was 40*s after adding the MH cover.

I use my truck about half the time running empty or small bed loads and the other half towing loads anywhere from 10-18K.


sabersix - I doubt you use your 4x4 the way I use mine, I am in 4x4 pretty regularly, I rack up quite a few miles annually around my ranch, local roads with constant snow during the winter, and usually a monthly 4x4 outing with friends in some tough places. At my first diff change, 15K, my front fluid was in much better condition than my rear fluid, at 30 K they were about even, at 45K they were about even as well. I had some metalics out of both diffs in my first change, of course, I was on the factory fluid then, none since going to the Amsoil fluids.


CD

 

The issue with the front fluid is that the axle is always turning, so even in 2wd you are generating heat. Heat causes fluid breakdown, which causes wear.