I serviced the diffs yesterday and used Chevron 75w-90 Full Synthetic in both ends, as well as a rountine engine oil change with my regular Penzoil 10-30 conventional.

On my way home today i averaged 15.0mpg at 60mph on about 7 minutes worth of highway. i cant honestly say i checked the mpg just previous to the service, but it was around 12mpg 4 months ago. i dont know if this is some magic oil or my truck is posessed. maybe the temperature change affected it that much?? but really, who cares? im gettin 15mpg!!! lol

 

The new oils make every thing run better/smother. I know when I took mine in to get done the guy said dana's don't like synthetic in them. I'm pretty sure it was that dana.

 

It may also have been a fluke. Wind may have been pushing you.

I hope it wasn't, I hope you get 15 mpg forever, but I am a pessimist at heart when it comes to vehicles.

 

lol, i am fully expecting to go back to 11mpg, i just wanted to share the good news, lol

 

i dont get it. there is no reason that a synthetic oil would be worse than conventional in a differential. did the guy tell you why Danas dont like it?

 

I don't know if you watch xtreme 4x4 on spike but they just did a Dana 44 and he used royal purple synthetic in it. I know that even though it is an informational show that they mess up sometimes too but I have used it personally in all of my vehicles and never had a problem. The best thing you could do is search the web for the manufacturer and see what they recommend or agree is safe for use in their axles.

 

sorry, but i think you're celebrating false hope.
i can also get great mpg on the highway at 55 or 60, up to 17-18mpg.
but around town stop and go, its more like 10-12-13.

gear oil service is a good thing to do, but it won't affect mpg very much.

 

just wax your ride if you want better MPG's....

and drop a Prius engine in it.

 

Yeah I've used Royal Purple fully synthetic in my D44 up front since I first did the fluid change. It's been quite a while now. I did use it in the rear until I had the Auburn LSD put in. It says not to use Synthetic so I just use Lucas non synthetic in the rear and the Royal Purple up front.

 

I would attribute most of the difference to temperature change, since the 12 was from 4 months ago and the 15 today.