The directions at:

http://mywebpages.comcast.net/xterra/tech/Diff_fluid_change.txt

were awesome. I changed my rear differential oil last week with no problems.

Since then, I've been experiencing dramatic improvements in gas mileage.

Usually, on a full tank, I get about 250 miles and then the fuel light goes on. Since changing the rear diff oil, I've had to fill up twice and the fuel light came on when I was closer to 300 miles.

Any comments on this? I have a 2000 XTerra 4WD and usually run the vehicle in 2WD high mode.

Thank you.

Wow, you must have had a sludge fest going on in your rear end.



A 16% jump is kind of a huge jump for a diff juice change...even going from dino juice to synthetic won't jump that much.

So - IF the old stuff was SO nasty and overdue that it was more tar like than it was suposed to be, etc...it sure is possible though.

My suggestion is that this means you might have waited a tad long to do this...and perhaps maybe you'd think about another change out sooner?

20% (50/250) is even more impressive!

Did the 1st gen. come with non-systhetic or synthetic in the rear diff? Which type did you put in? Did you change anything else (fuel filter, air filter, driving style, etc.)?

Funny, I looked at it like the 300 miles/tank was the baseline, and that he LOST 16% of his mpg dropping to 250....but yeah, to go FROM 250 TO 300, he would get 20% more mpg.

If the average fill-up on a 19 gal tank is say 15 gallons (Reads empty...with a reserve...), 300 miles on 15 gal = 20 mpg.

That's about what I average as well, 20 mpg.

250 miles on 15 gallons = 16.6 mpg.

So, jumping up from 250 to 300 miles: That's a 3.4 mpg improvement!

I'm not sure what kind of oil the vehicle came with, but it was almost 40,000 miles overdue for changing the fluid. I have almost 68,000 miles on the vehicle presently and the fluid has never been changed until last week.

I didn't notice it being sludgy or anything, but there was a fair amount of metal shavings on the plug.

I put in regular, non-synthetic Valvoline 80W-90 into it. I didn't change anything else and my driving style hasn't changed either.

The air filter is next on my list, since it has also never been changed. I really wish I had changed the rear diff when I got the vehicle. I didn't realize it was that easy.

I think if I found my air filter was in any way dirty I would be changing that first. I am due to change my diff. I can only hope I get some sort of MPG gain.

What brand of fluid does anyone suggest to use for the diff's and the transfercase???

Dont forget, summer go juice is comin back onto shelves. 20% is a little too much for just a fluid change.

Not possible.

I agree, summer blend is now coming back and the temps are warming up. Both these things have a much more noticable affect on MPG than the rear diff. Even if you were running wet cement in that rear diff, you would never see that kind of MGH change from just the rear diff.

Hell, if there was no rear diff and the rear was floating on air there sill couldn't be that much of a change on it's own.

For the two fillups after the rear diff change, the fuel light went on around 280 miles. But the last fillup, it went on at 253 miles.

my nissan dealer did not have in stock the rear dif oil, went to auto part store and i believe i purchased a bad blend....my mileage has dropped considerable..... what type of non nissan oil should i replace it with????

Hi Guys,

The weather has finally broken and I'm also going to change my x's fluids. But what kind of gear lube I should use? I want to use Mobil 1 syn but I couldn't find it in 80w90 only in 75w80. Is Mobil 1 an ok gear lube to use or should I get something from the Nissan Dealer?
I was also going to buy Mobil 1 ATF is that ok compared to the Nissan dealer stuff? And if I do use Mobil 1 do I still have put the 4oz of friction additive in? What do you recommend I use for the fluid?