Went to get in my car to drive to work this morning, and noticed a very fine covering of what must be 'soot' particles on my dash.
I had started it about 15 minutes earlier and left it to idle until I drove. Anyone had this happen? Is this possible? What my cause it? Anything to worry about?? Thanks

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1981 300TD
1985 300TD

There are foam seals in and around the cabin air distribution system. They disintegrate into sediment. Someone who knows the vehicle can suggest where to look. Otherwise start with the recirculation flap and the hose from the cabin air temperature sensor to the blower housing.

Sixto
87 300D

Good call.
If it is dry powder that does not slime, it is dead foam sediment blowing out.

.

If it is soot it would almost certainly require two things - an exhaust leak and a compromised seal or hole in the firewall or floorboards or entering through the fresh air vent... assuming of course that the windows were rolled up.

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Generally that is a bad intake/exhaust gasket and/or the down pipe flex joint.
The leaking exhaust is sucked in the climate control fresh air intake.

.

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has it rained lately? this happens to me when debris sits in the car and decomposes... the cowl vents in front of the windshield are nice nesting places for leaves/grass clippings etc, and some of it sits down there until it rains, and gets stirred up, then we start the car, and the heat comes on in defrost, and the fine dust gets sucked into the system, and deposits itself on the dash... hose out your cowling, and it may go away on it's own... open the hood when you do it, and notice all the stuff that comes out the two drain elbows in the firewall...

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Hmm. I appreciate the input. It is definitely fine black powder, but seems particulate rather than slimy when touched.

Full disclosure. I washed her at the car wash yesterday. But I have done that every week in the three weeks I have owned her.
I will keep an eye on it. Thanks.

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1981 300TD
1985 300TD

The notorious foam tube would be a good suspect.

There's a piece of foam that connects the in-dash temp sensor to the blower. The blower draws air across a thermistor by vacuum. The tube breaks down over time. It's then in a perfect position to send foam particles into the blower to be distributed about the car. Do you Armor-All the dash? That might make it appear worse.

You can check the condition by pulling the glovebox liner out. You might be able to try the "tissue over the grid" trick. If there's good suction the tube is okay, if not, then maybe not. I don't know if this works on the W123 suction, but it works on other models.

I have used Aerospace 303 on the dash (it's in great shape) but this is definitely the first time I have seen these particles. They were spread over the entire dash in a very even pattern. Must have come out of the vents very evenly...

Is the sensor you are talking about the very small square vent on the top front of the dash?? I will try placing a tissue over it to see if it is pulling air.

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1981 300TD
1985 300TD

Yak gets the gold star for the day.
I pulled the glove box out today to aid in a speaker change, and what was left of the foam 'tube' disintegrated and fell to the floor. What a mess.
Now a new question. Apparently this foam connects the black tube return to the blower motor? Do I have this correct? Now there is no connection between the tube under the dash and the small 'vent' on the dash. Should I replace this with something? If so, what. Another foam tube? Why was it foam to begin with. Seems like a bad idea (for a car that lasts so long).
Thanks. This forum is the best.

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1981 300TD
1985 300TD

And the answer is? Envolope please..........

source for or replacement for foam tube on ACC w123

Charlie

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hi, i've got the same problem on my '83 300D and i'm going to replace the hose/tube. can someone please post a step by step process for replacing this tube? does it really involve removing the dash or can i do it without removing so many pieces? thanks.