Recently took the Jeep in for an oil change and they found the rear diff fluid to be black. It had been only 5k miles since the Diff fluid was changed during the 30k service. The front fluid was perfect. The only difference is I now have a 2.5in lift and 33's installed shortly after the 30k service. So only 5k with the lift installed. So I have a couple of questions?

1) What would be causing this? Shop told me could have just been super dirty, or have a bearing going bad.

2) Should I worry much about it? Shop told me it will be fine until next oil change and have it looked at then!

The shop changed the oil for free, so that was a pleasant surprise.

 

The simplest explanation is they did not actually change the fluid in the rear diff. Further proof of that is they changed it for free afterwards. No way it was "super dirty" in 5k miles.

I would not be really worried about it unless your diff starts making noise, but I would check the fluid every 1k miles or so. Go in through the fill hole, maybe with a straw and pull a little fluid. I bet it stays clean.

 

I know I just changed mine at 3821 and it was very dirty; both the front and back. It was the original fluid and I was surprised it was that dirty.

If you are not using 4 wheel drive much, would I be correct in saying the rear is going to get more use and would get dirtier faster?

 

Agreed if they just changed it it shouldn't be black. They probably didn't change it.

 

I thought the exact same thing, that they did not change the fluid, but I know they did. There was a new gasket installed, which meant they had to take the cover off, which would empty the diff. I wonder if they cleaned it or not when the cover was off, or just slapped the cover back on and refilled it.

 

mine was pretty dark when i changed it at 1000 miles. front was brand new. Comes down to it moves the vehicle. It's going to make heat, that breaks down the oil. I wouldn't say it should be black like tar at 5000, but the service interval is 15k...(i believe)

'cleaning' the diff shouldn't make much difference. If it's new fluid, just change it at 15k. There is probably nothing wrong with it...

2nd, why the hell aren't you doing this service yourself? If you change your own oil, you can certainly service the diffs. If not, then "alright" lol

 

Is it really dirty or black like tar. I bet yo have the posi(with clutches). if so, the clutches are worn, causing the black fluid

 

Simply just lazy

 

Black like tar

 

I change my diff fluid once a year, besides the original break in fluid every time I change the "old" fluid comes out clean as honey. I'd have a bet it wasn't originally replaced. I just did my diffs after 22K and the fluid looked like new. Hummm....

BTW I have changed the fluid 3 times now and its always "clean" looking.