Wondering if anyone knows if this is a common problem and where it might be coming from. I seem to smell it more if the heater is on and blowing air. Definitely much stronger if the car is stopped in traffic than on the freeway.
Where is the air intake for the heater air blower? I guess that is a place to look for an exhaust leak nearby. If I keep the cabin air re circulation turned on, then yes it prevents the exhaust intrusion. Is there a way to definitively find an exhaust leak using smoke or soapy water or something?
1987 300SDL

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1987 300SDL

On my 240D, I see smoke emerging from my exhaust leak when it's running cold. Might just peek around under the hood and see what you see.

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"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

This sounds like two distinct problems: you have an exhaust leak and you have a way for that exhaust to get into the cabin...

I'm not very familiar with your chassis, but on my w123 the battery sits in the right rear corner of the engine bay, near the heater box, and somewhat above the exhaust manifold. If yours is in a similar location, (or even if it's not) you might consider pulling your battery & tray to inspect for a hole in the firewall (rust likes to form under & around batteries). If you find one, let me know and I can provide some suggestions on how to patch it without welding if you'd like.

As far as where you have an exhaust leak, you might try holding a piece of tissue around the exhaust flanges & fittings with the engine running (be safe, use common sense, etc) - if the tissue starts blowing around, that's a likely leak.

Do not know your car but on my 300SD there is a plastic pipe that goes across the air cleaner. It attaches to the air cleaner via a rubber connector on one end but the other end slips out sometimes from the other connector. That is when I get exhaust in the cabin.

Does your have this set up?

Have you looked under the hood?

Does your engine shake a lot? I have three or four year old mounts on the engine and a new engine shock mount and mine never shakes loose.

I need to put new nozzles in the injectors too so it does shake a lot. I've rattled a few of the breather housing mounts apart but I've always bought the cheap ones.

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84 300SD
85 380SE
83 528e
95 318ic

My SD had similar issues, turned out the exhaust flex pipe had failed.

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83 SD

84 CD

open hood... look on the exhaust manifold, 2nd cylinder back from the front... there is a small bellows that ALWAYS cracks... it will limit turbo boost pressure also.

another possibility is downstream of the turbo is a flex connector in the main exhaust pipe... they break as well. either one would dump exhaust into the engine compartment and allow it to pull into the heater intake vent.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Fix it sooner than later. The fumes can make you sick and are carcenegetic as well. If you cannot find the leak any muffler shop should locate it fast.

Taking a closer look, the dry black powdery soot should have been a giveaway, but now I know. I can't tell exactly but it looks like it's the brass coupler that joins the two sections of the exhaust manifold. So on another car I have removed and replace this part before for a turbo rebuild, and I'm wondering is there supposed to be some sort of sealant, putty or gasket that goes in there, like a washer, between the brass part and the cast iron of the manifold? It seems I'll check if this became loose, or if it is cracked or what silly thing is going on here. This seems to be the logical place source where the exhaust in the cabin's source. Thanks for all the suggestions here~

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1987 300SDL

The attachments may help.

Attached Thumbnails

     

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83 SD

84 CD

yeah... nothing in that image covers the exhaust manifold section bellows...

he's talking about this...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I see, the FSM doesn't have anything about that, it shows a four cylinder exhaust manifold, maybe part of a V-8, but in the 87 SDL section.

Attached Thumbnails

 

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83 SD

84 CD

Exhaust manifold image

Attached Thumbnails

 

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

^ Thanks.

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83 SD

84 CD

So I'm wondering can I replace the part 278 (in the schematic above) without having to remove one of the exhaust manifolds. That tube 281 would have to slide left or right and I don't think it will. I remember the only way of getting the exhaust manifold off is to pull the head.

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1987 300SDL