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Transmission noise?

I have a 2004 Frontier Crew cab long bed with manual transmission and approx. 160,000 mostly highway miles.

I noticed several months ago a low level “hum” when driving through the mountains. A day or so later I was traveling on the highway and noticed a strong smell of possibly overheated fluid. It seemed to only be noticeable when I put the windows down to let air in.

Since then I have noticed this smell a lot when traveling long distances. I always smell it the strongest when I stop at an intersection after traveling at 70 mph for an hour or more. I have checked the engine several times to try to locate the smell but it seems to go away quickly.

I have checked the power steering fluid, antifreeze, changed the fuel filter and replaced the differential fluid but the smell still persists.

I travel long distances a lot and sometimes the “hum” can get pretty loud when I enter a town and go into the lower gears.

The most recent occurrence is that I have noticed that after driving for long periods at 70 mph a faint “rrrr” in the transmission when going slowly in the lower gears or at a traffic stop. There has also been a higher pitched noise a few times when accelerating quickly in the lower gears.

I had a '95 Frontier w/manual transmission that did a similar but louder “rrr” noise in the lower gears when I traveled long distances but no smell. It turned out to be a bearing in the transmission.

I believe that the grease go hot and caused the noise. The warranty handled the repair and I think the bearing was replaced.

When I had the fuel filter replace recently the repair guy said he had a similar problem with his Frontier w/manual transmission.

It seems the smell is getting worse and the high pitched noise is still very rare but is causing me concern that I may be ruining the transmission.

Does anyone have any input or experience with this? I would really appreciate it. I am 1,600 miles away from home and would like to make it back without ruining the transmission.


can you describe the smell a little more completely? Overheated fluid can cover a lot of different smells, from sweet to fishy.

From what you’ve said, I’m suspecting your transmission might be getting too hot. If that’s the case, it might indeed damage the transmission if you try to drive it 1600 miles.

Is the oil level correct in the tranny? More than likely it is dripping on the exhaust and burning off. There should be residue on the pipe. It could be under the hood, but you would smell this with the fresh air intake open. Could be valve covers or any number of seals. Get under it with good light and look for the oil and trace it fwd until you find your leak.

It is a sweet and pungent, burnt odor.