Burning odor after using 4wd

So, with the Winter finally upon us, I got a chance to put my 2000 X into 4WD for the first time in a while. After driving it for a little bit and coming to a stop, I began to notice the distinct odor of burning rubber. I shifted out of 4wd and drove it in 2wd for a while and the odor went away. I initially thought it may be linked to the condenser unit (Nissan told me 2 years ago it was going bad and will go out at any time......still hasn't officially gone out yet and I still have my A/C in the Summer months), but it only seems to happen after driving in 4wd. The odor is not present if I'm driving in 2WD.

Anyone have any ideas on what it could be? T-case issues? Front Diff issues maybe? Anything?

Thanks in advance!!

I'd look at what is in motion/use in 4wd that is not in 2wd, as a starting point.

As you seem to be implying that you have since driven in 2wd, and there was no odor, and, it is implied that you can shift into 4wd, get the odor, shift back to 2wd, and the odor goes away...the 4wd added involvement should be the key.

If the above implications are not known, or wrong...let us know, or, take it out and go back and forth between 2wd/4wd enough times to be sure.

TJ, based on what I've experienced with it recently, I'd say you hit the nail on the head. The odor is not present when in 2wd, begins shortly after being put into 4wd, and disappears again after shifting back into 2wd. That's why I'm thinking wither T-case or front diff.

I guess I'm just curious if anyone has experienced this, and if so, what did it end up being?

It sounds like you've narrowed it down, I'd check the front Xfer case fluid (level & condition) and look out for signs of anything that may be rubbing up there..

But since it's winter outside I want to throw one more thing out there for you to consider...whenever we get snow out here the road crews do a really good job of putting salt & brine down. The slush and brine mix tend to cover everything on the underside of my Xterra including the hot exhaust system. After a little while of driving in that stuff(when everything heats up) it does give off a slight burning odor - and I usually happen to be in 4WD at the time b/c of the conditions...

It's pretty obvious to me that the odor is that salt brine getting splashed up all over the hot exhaust and yes, we get it on 2WD vehicles as well but not the same extent, simply because the 4WD vehicles always seem to find more and deeper snow to go play (I mean drive) in...I wonder why that is...

-Saturday

OK...Now, I don't think it's anything with the 4wd system or front diff or T-case.

Now, the truck is giving off that odor whenever it's driven and I came home to find a few fresh puddles of motor oil on the driveway (only spot where there's any oil on my driveway now) where the truck stood last night. I checked the oil this afternoon when I filled up the gas tank and didn't notice anything out of the ordinary. Looked normal (not milky) and levels were fine. Only thing I did notice was an oily substance that seemed to be leaking out of the top of the engine on the passenger side. I'm wondering if my head gasket is giving me warning that it's time has come.....

Oil from the top is usually a valve cover gasket, but could be the intake or a head gasket as you mentioned..

If the oil originates from where the transmission mates to the engine, then it's likely a rear main seal, also fairly common...

also check the PS lines, transmission, and brake lines, etc.. make sure it's motor oil..

Good luck,
-Saturday

Ended up being bad valve cover gaskets (Good Call SM!). Oil was leaking out of the valve cover (which would explain the oil on the top of the block) onto the exhaust causing the burning. Wasn't anything in the driveline or head gasket (Thank God!)....

Thanks for all your help!!

Was it a bad gasket or just loose bolts holding it down.

They can loosen up.

Carlton, I think that's still you, correct?

Well.......its become an odd situation. I was helping a buddy work on his 91 300zx TT and we got to talking about the X. He is friends with the mechanic that worked on my truck (he used to work at the dealership) and told me he saw my truck on the rack and commented on it. to the mechanic. The mechanic told him I had actually cracked the valve cover!! Now...I don't know how true that is because I didn't see valve cover on the writeup and the cover is far from new. I can see a new gasket sticking out from the cover though, so I know it was at least only a gasket issue. Running great now though!!

Yup.. still me.

Not sure how you would crack a valve cover.