Transmission fluid smell in cabin

Over the last few weeks I’ve been smelling transmission fluid in the cabin, especially when the vents are blowing in air. I also smell it outside of the car after driving for a while.

I wasn’t sure what would be causing that (breather valve issues?), and whether it is more likely to be the transmission or transfer case given that it comes in the vents so clearly. It’s not due to a leak.

Any thoughts?

 

Trans and xfer take two different fluids. Can you distinguish trans or gear oil smell?
Check the levels? Visual oil condition?

 

I used the Motorcraft in the transmission and the Redline GL5 75W90 in the transfer case. My recollection is that they smell basically the same, but maybe my memory is wrong. Either way, I am very familiar with GL4 transmission fluid smell and it’s like that.

The smell is definitely heat related since it only happens when everything really warms up.

I haven’t checked the transmission fluid level, but there are no leaks and I put it in last year. I’ll try and check the level soon. I did look at the transfer case oil and it looks about the same as new (also replaced last year).

 

Have you inspected your pivot shaft seal?

 

I have been meaning to replace the seal in addition to the breather valve (I have all of the parts).

The transmission is a used one I bought back in 2020, and when I installed it for the first time last year there was fluid building up around the breather valve. So I put a bit of a hole in the rubber seal in the breather valve and everything was fine. I’ve been meaning to replace the parts but it’s been working great since then. No apparent leaks.

 

Well perhaps the time to finally do it is now when you check fluid levels

 

It could be aeration due to an over fill issue. Not that there's a pump in the manual transmission but with gears meshing it's supposed to be more of a coating than submerged.

If it's submerged bubbles begin to form and create pockets of air. Maybe that's what you're smelling in the cabin?

I had a customer once who brought a Lacrosse in since there was a "fluid leak in the door." As soon as I got in the car it reeked of something. I found a bottle of Cocoa Butter that fell over on its side and coated the entire door inside/out, inside the panel, the carpet.

You sure you didn't spill anything or have some food get lodged somewhere causing an odor? Anyone else confirm the smell?

 

Thanks for the thoughts. It only started smelling recently and I filled it 1.5 years ago, so it doesn’t seem like it’s be an overfill situation. But maybe it’s only showing up now? I have always just filled a transmission until I get a dribble out the fill hole.

Others have smelled it, but they don’t know enough about cars to know it smells like transmission fluid.

 

Id look seriously at the vent and pivot, like Awa said. If you have no external leaks, there isnt really anywhere else for it to come from, short of an input seal which might not be a visible leak yet.