Cabin Fumes
 

Hello!
My '81 300SD recently developed a very irritating problem.
You can really smell fumes in the cabin when you stop at a light.

Car runs great with minimal smoke except when floored.
The diesel smell/fumes inside the cabin is really irritating and gives a head ache. Also, after alighting from the car my clothes smell like diesel fumes.
Would like to request for leads on where the fumes are "leaking" into the cabin. Also, what can I do to prevent the fumes from entering the cabin.
Thank you.

I assume you are talking about exhaust fumes in which case I recently had this problem with my '85 wagon except that I could only smell the fumes when I had the sunroof open. The problem was a hole in the top of the forward muffler that was allowing fumes to accumulate under the car, even at fairly high speeds. When I opened the sunroof it created a vacuum that drew the fumes into the passenger compartment around the rear of the car. When I replaced the exhaust the problem completely went away. I discovered the leak by crawling under the car with the engine running and feeling all around the exhaust until I could feel the leak. You may want to do this with a cold engine/exhaust and obviously block the wheels really well.

If you're looking for an exhaust leak, covering the tailpipe should make it easier to find the leak.

Sixto
91 300SE
87 300SDL
81 300SD

LRG, thanks!
The odor of the fumes is present even when the windows and sunroof are closed. I agree that the odor intensifies when the sunroof is opened.
Any other possible sources of the irritating odor?
Sixto, Mabuhay!

I agree that it's exhaust. Granted the rubber seals around the car (doors and windows etc...) are old but there must be a leak letting fumes out under the car and maybe some of it comes through the vents. You could even have some floor pan rust letting in even more fumes.

edit: I just realized you are in the Phillipines so maybe you have no rust....mybad!

JOJO126,

Check your injector return lines. Leaking return lines will contribute to fumes in the area of the cabin air intake. If you run with AC all the time as I imagine you do this time of year, lock the air intake in the recirculate position. Remove the glove compartment to expose the vacuum actuators and levers. It won't be difficult to figure out how to close the flap for good.

Some might argue that MB doesn't allow full closure of the flap for a good reason. There are enough leaks in your car to ensure that the carbon dioxide that builds in the cabin is replaced with carbon monoxide from outside ;)

BWatson,

Rust is a very real part of life in the Philippines.

Sixto
91 300SE
87 300SDL
81 300SD

Everything in the Philippines wants to corrode or rust away. Even if your car is sitting in the garage and out of the rain, it will rust. It is easy to get pin-holes in sheet metal, especially the muffler and exhaust system. If this is the problem, you should replace it with stainless steel. I assume you'll want to keep this car around for many years, and stainless is worth the extra cost. You could have some fabricate a new exhaust system for you.

Anyway, it always smells like diesel smoke in the Philippines since everyone drives a diesel!

Sixto, as usual your the tips are very helpful. Mabuhay! I will check on the aC dampers this weekend.
Mr. Watson, I will also check the exhaust. Maybe put the car in a lifter and check for holes in the flooring as well.
Mercedes Man, yes everything does smell like diesel in Manila because eveyone uses diesel... sounds like your from Manila also.
The problem is the diesel fumes in the cabin really give a bad head ache. The car has been parked in the garage for 2 weeks as the odor is unbearable during traffic. Bigger problem is if you open the windows the jeepneys get you with more fumes!
I'll check all the leads this weekend and will get back to you guys.
As always this site is really helpful specially to non-mechanics like myself.
Thank you very much again!

SORRY I wasnt able to check out the car this weekend as I had my son baptiized and was pre-occupied with the preparation. Will get back to you next week. Again, Thank you.

JOJO126,

I did not notice that you confirmed the smell is exhaust or vaporized Diesel fuel before it is burned. In either case, the way they typically enter the cabin is through the ventilation system. The air intakes are at the base of the windshield, and the hood is not sealed to the fenders when shut, so anything in the engine compartment is free to exit through the gaps in the hood and get sucked into the ventilation system. This would suggest your odor is coming from the engine compartment and not underneath the car. If it is exhaust, I would expect a little elevated noise level. I just had the intake and exhaust manifold gaskets replaced on the family 240D. The engine mounts failed and the engine bounced around so much starting the car that the exhaust manifold studs got stretched/strained and the car developed an exhaust leak. It was pretty loud, and it did enter the cabin area, but it was not severe enough to make clothes smell or give you a headache.

On other occasions I have had the daisy chained injector bypass lines fail, especially the plug on the last cylinder's injector, and had pretty serious stench of Diesel fuel, not exhaust, enter the car. When they leak and the car is running the fuel evaporates when it gets on the head or block and you get a steady stream of fumes that come into the car through the ventilation system.

The fuel filter connection may also be leaking. I have had that happen before, same result, a stink in the cabin that is very unpleasant.

Just some ideas, and congratulations on the new son! Jim

I had a similar problem earlier with my car and found that the flexible rubber around the gear shift was split all around, leaving an opening from underneath the car to the cabin. Replacing that seemed to help a lot.