Originally Posted by Doss
That's nice and everything, but are you still under warranty? If you are, I'd run what Ford says to.
I'm running Mobil 1 syn in whatever weight the manual said to run.
Also, with a lot of things, any time someone did a test "years ago" on the current state of tech in a moving field, I throw that out the window (usually) if I'm applying it to today's tech. Another thing, if no one else did testing to support it (or even against it really), I'd be a little suspicious. That's my nature as an engineer and scientist. I'd have to know all the parameters, what the meaningful measurements are, and the test controls/conditions/etc..
Years ago doesn't mean 30 years really. Synthetic diff fluid and normal diff fluid hasn't changed over the years. The concept of how an axle works hasn't changed over the years either. Currie Enterprise is not a company I would argue with. If you know little about them they build and design axles, third members, suspension items, and on. The owner helps design things, and uses his own stuff to win rock crawling championships. Wheeling puts a greater shock load to an axle than driving down the road towing anything. The rear axle that comes on the Jeep (d44), so far i have rolled the stock splines, broke a chromoly shaft, and rolled the pinion splines some with only 35's. They an example of shock loading.
They did the test to find out why they were having to warranty axles so much. They found out that synthetic fluid does not pull heat away from the R&P causing failure. Just because Ford puts in the manual doesn't mean it's the best thing to use. For example, I have read where it recommended to use rad fluid other than Fords.