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HELP: Burning Smell When Heat is ON

23K views 11 replies 9 participants last post by  ss2715  
#1 ·
A bit of an odd "problem" here for several reasons, and some help would be greatly appreciated!!

It is/has been winter here in Chicago for a few months, and since ~November or so, when I crank the heat up all the way and drive around the city, a very strong burning smell comes through the car. A bit about isolating where it from/what's causing it:

-It's not a sweet smell like many fluids/leaks may give off. It's more like a rubber-burning smell.
-It disappears at higher/highway speeds, presumably because whatever is burning/causing the smell has enough air passing over it to keep from entering in the car's venting.
-It can be smelled from the outside of the car while parked - and is coming from near the passenger side firewall, when the hood is open.
-It is not the cabin filter - mine was new, and when having service done recently, I mentioned this problem, and they replaced it - to no avail.
-It's not immediate - the car has to warm up (10 minutes or so), and be above an idle. I know this as I tried to replicate the problem by having it on for ~45 minutes to warm in the cold, with no results. It was only when I hopped on the pedal for a minute or two to get the RPMs up a bit, that the scent returned.

I describe this as a "problem" as the car is 100% otherwise. All belts are new/in great shape, fluids changed, etc (about 70k miles on the car). Nevertheless, any burning smell usually evokes concern! There is nothing touching/rubbing any hot areas of the engine or exhaust that shouldn't be/otherwise isn't - which would cause this. My only thought is recently, my car had the windshield changed several times (3 in fact by the morons at Safelite - who say they have the OEM glass, but in fact don't/the rain sensor will never shut off - and once by the dealership who finally got it right). This was around September/October, and the last time the aforementioned morons did it, they did a very sloppy job, leaving the black tar-like glue on the hood of the car, and (without telling me, hence a nice dealer trip thereafter), having to break out one of the windshields, getting glass into the wiper motor area, and burning that out. So, my thought being for an otherwise 100% healthy and well maintained car, maybe the morons or stealership people got a little crazy with the glue/parts and dribbled some down in an area that gets hot, and that's what I'm smelling. I can't find anything when trying to track the smell down/look closely.

Lengthy, but please, any help would be tremendously appreciated, as a burning smell now, could mean big problems, later.
 
#3 ·
... when I crank the heat up all the way and drive around the city, a very strong burning smell comes through the car. A bit about isolating where it from/what's causing it:

-It's not a sweet smell like many fluids/leaks may give off. It's more like a rubber-burning smell.

-It can be smelled from the outside of the car while parked - and is coming from near the passenger side firewall, when the hood is open.
Could it be the smell of overheating wire insulation from an electrical fault somewhere? Burning plastic insulation has a characterisic smell. The area you describe has a collection of electrical modules under a cover. Why not remove the cover and have a good sniff inside there?

See the WIS drawing below:
 

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#4 ·
I'll take a look, keyhole. I know about the electronics in there, but didn't think that would be the culprit based on the circumstances that it seems to arise from (but I've got nothing in my cards, so I'll shoot for anything now!).

Keep me posted, Volker - I had previously assumed it was just from being behind a truck at a light, etc. It's closer to a burning rubber smell, not so much oil, though. But I only started to notice it when temperatures here hit ~15 degrees or lower (I wish I could tell if there were any correlation, but it's been so cold this winter for so long, I haven't had the chance!).

Still open to any other thoughts/considerations/input!
 
#5 ·
Unfortunately, all is clear and the smell still persists. It seems to arrive rather quickly now, though not as strong. Often I barely notice it now while driving, though once parked and walking away, the smell of burning of some sort still persists.

While I would like to think its getting better as the burning smell is less prominent, I don't think any Mercedes story that includes "burning smell" in any capacity ends well. Input still appreciated!
 
#6 ·
Mine as well update despite nothing assisting in pinning the problem. Into the warmer weather and the smell is continuing. Doesn't seem to matter whether or not the heat or AC is in use. Still have a 'burning smell' coming into the cabin when at low speeds (at higher speeds it seems to dissipate enough to not be smelled in the cabin so readily). However, upon parking and exiting the car, the smell is then somewhat readily noticeable.

As you're facing the car at the front, the smell is definitely originating a bit left of center and back almost all the way to the firewall. It now has been to 3 different mechanics, all saying that noting appears to be wrong.