So I did my 60k maintenance this weekend and when I drained my front diff, the first thing I do after pulling the fill plug is to stick my finger in to see where the level is. I got my trigger finger all the way in and down before I felt any oil. Hmmm, then I drain it and it looks like fresh oil. I have my 45k service done at the dealer as I was still in a sling. So this oil has been in there, looking untouched, for 15k miles!

So here are the questions, obviously I know the fluid was low when I drained it, but what does the clear new looking fluid tell me? That is was so low it was of no use at all, I imagine? Does the oil in the front diff get much less wear if you aren't in 4 wheel drive? What damage should I be looking for? When it drained and I checked the magnetic drain plug, there was very little shavings. No big chunks when I took the cover off (to put on the new ARB) either. Visually everything looked fine.

The rear was full to the fill plug when I did that one, and it was as dirty as I would expect gear oil to be after 15k. <shrug>

And now the damnedest thing, I had been a pretty solid 15mpg and now after swapping to Mobil 1 5w20 synthetic and the royal purple 75w90 in the front and rear, my mpg seems to have dropped to 14.2!! What the hell? Now my front is properly lubed AND with a better product and I'm getting worse mpg's?

 

Out of curiosity, how much oil did you use for the front vs. rear?

To try and answer your question, I believe the gears won't get worked up that much unless you are in 4wd. When I changed mine out the first time, my rear was nasty and my front was not new looking but nowhere as bad as the rear. I had done a bit of wheeling as well as snow driving so i used 4wd quite a bit.

Can't comment on the mpg loss...too many factors can cause that.

 

I used 2 pints in the dana 30 in the front with the ARB and the stock rear took just under 4 pints. I think the rating for each with my configuration is 2.1 in the front and 3.75 in the rear. The rear is simple with the stock cover as i fill it until it starts to dribble out. The front, I will check again tonight after 100 miles and maybe add the remainder left in the bottle from the rear.

In my simple mind, I would rather overfill a little and blow it out the overflow hose than to under-fill.

I haven't used 4x4 since the last change 15k miles ago. I know, I think I need to start a new thread for that. Hi, My name is Dan, I haven't been in 4 wheel drive for 4 months.

I will watch the MPG, I am assuming the engine will just need to get used to the new oil as it strips out any additive build up form whatever the dealership had been using. I read a lot about people getting an extra 1 or 2 mpg when switching their diffs to synthetic. As a skeptic, I wasn't really expecting a gain, but I certainly wasn't expecting a loss.