Pungent smell in cabin after replacement of clutch

[Cicloturista]

I have noticed it just the day after replacement of clutch, after a 150 km highway trip. It was the beginning of summer and since then this began to happen every time at the end of long journeys. Then, in winter it seemed disappear but it came back again in spring. The man who replaced the transmission thought a mouse or a small animal has entered and die in the air ducts and cleaned them and washed the engine but he did not find anything. I brought the car to another Nissan garage after driving for a while in order to make them smell and they told me that smell could be a transmission oil under the gear shift or anorther kind of oil, in case very difficult to clean. They also put the car on a ramp and looked under the car. They noticed in the mid section a small space on the exhaust system with traces of smoke where 2 pipes separate. They fixed them and gave me back the car. But problem still occurred. Again a third garage has not solved the problem and now, after 2 years, smell appears even after short journeys and also in winter. It is not typical oil burning smell but a kind of acrid, pungent smell, like plastic burning or garbage, or a mineral oil, for someone also like ash in ashtray. Hard to describe. It appears when I slow down and open the car windows, even not completely. It seems to be more pronounced on the driver side. It seems to come out from upper air ducts but not sure and I do not smell it through the air ducts when A/C is on. Terrible smell if I switch off the A/C. Once began, If I close the windows the smell becomes terrible and I have to switch on A/C to stop it. But it seems not coming from outside the car. No smell outside, or around wheels or engine. Anyone can help?

[centralcoaster33]

Hi and welcome to NICO Club!

While there could be clutch smells with a new clutch, that would go away after the clutch was broken in (seated, bedded). That smell is a lot like brakes cooking, a sort of hot metal smell. Perhaps the mechanic had to remove other parts to get to the clutch and didn't put them back properly. Pungent and dead animal go hand in hand. You could have a dead rat and nest in the cabin air filter parts. Have you had anyone get into your climate control duct work and look for things that shouldn't be there, like dead animals?

Old oil and coolant mixed with road dirt and grass can create a sludgy grimy substance on the bottom of the engine and car. When heated up, that can stink as well. You can usually see a bunch of gunk on the bottom though and having it pressure washed can fix it. Well, that and patching whatever was leaking fluids.

[Cicloturista]

Hi, thanks a lot for your reply.
Garage man who replaced the clutch has checked the air ducts and, he said, he also cleaned them, finding no rats or other animals. The second time he also washed the engine. A different garage also checked the car and they told me that maybe when clutch was replaced someone could have filled too much transmission oil under the central part of the car and that is very complicated and expensive to remove and clean excessive oil that could be under the part between the front seats. But now, 2 years passed and the smell appears even very early, after 15 minutes driving and is increasing. in any case i expected a decreasing after 2 years, even in case of dead animals or excessive oil. I am thinking that it will be necessary to replace again the clutch and check every component. May a clutch part contain a particular smelling product? They assured to have installed only original spare parts, but now I am not sure. The second garage told me that is impossible to verify if the replaced clutch is an original Nissan spare part or not. I do not understand also why the smell appears only opening a window (left or right side). Then if I stop the car, open immedialtely the door and smell outside, I do not smell any smell. I really do not know, but I have 3 sons and I do not want to have long journey anymore until the problem is solved....

[centralcoaster33]

This does remind me that some types of transmission gear oil and differential gear oil can smell like dead animal... kind of anyway. It is more of a pungent smell. You've been around the block a time or two with this smell. Maybe it would be okay to have a normal service done at a shop. Have them drain and replace your fluids in the drive train. Have them let you smell those fluids to see if it seems like the smell you recognize.
There's a transmission, a differential, and if you have 4 wheel drive, a transfer case and another differential. Have them clean up each component a bit to get the old grime off of the case.

You can't do much with a clutch short of taking off the transmission to get to it. If you do take it off to inspect it, you might as well just toss in a new clutch and pressure plate. I think you'd have slippage if there were any of these oils on the clutch, so I suspect you're fine there and don't need to get into it.