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  #1  
Old 05-23-2019, 12:54 AM
Desert Panther's Avatar
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Location: Avra Valley, Arizona
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Question 85 SD diesel exhaust fumes mystery

1985 300 SD in well-cared-for shape. Car runs fine, no complaints with that. But when cruising at any speed with any or all of the windows or sunroof open, the smell of diesel exhaust comes into the car. This doesnt happen with the windows and sunroof closed, so I know it doesnt have an exhaust leak.

It is mind boggling (to me, anyway) that at 70 MPH on the freeway with all the windows closed but the sunroof open, that the exhaust fumes somehow travels up over the rear bumper & tail light panel, forward over the trunk, rear windshield, back section of roof and finally into the cabin! How is this possible?!?!


What would you suggest to remedy this issue, I am completely stumped.



NOTE: Prior to my ownership, somebody had replaced or re-welded the rearmost section of exhaust pipe and it isnt 100% aligned perfectly, but its really close. I cant imagine that would cause this issue, but I've been wrong before. Can anybody knowledgeable with these cars or this general situation, chime in here & enlighten me?
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  #2  
Old 05-23-2019, 02:43 AM
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Quote:
Originally Posted by Desert Panther View Post
But when cruising at any speed with any or all of the windows or sunroof open, the smell of diesel exhaust comes into the car. This doesnt happen with the windows and sunroof closed, so I know it doesnt have an exhaust leak.

That's interesting logic.....have you actually checked? You probably won't smell exhaust with everything shut if the leak is rear of the intakes below the windscreen.
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1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...not yet legal
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1977 280> 300D - 500,000km+
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  #3  
Old 05-23-2019, 02:43 AM
vwnate1's Avatar
Diesel Dandy
 
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Look at the rear bumper mount surrounds ~ whey they're damaged / missing or loose, the exhaust fumes get sucked into the trunk thence the passenger compartment ~ look at the carpet on the parcel try around the first aid kit ~ there's usually some amount of exhaust smoke staining it .
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Old 05-23-2019, 08:27 AM
t walgamuth's Avatar
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Location: Lafayette Indiana
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Check your connections under the hood....at the down pipe to manifold connection and especially around and in the flex pipe. Leaks there are hard to find sometimes.
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Old 05-23-2019, 09:04 AM
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wish I could smell it again,really liked my KFC oil,burning in the motor
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Old 05-23-2019, 09:24 AM
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When that happened to me in my 300SD, it was the plastic vent pipe that fits into the top of the air cleaner with a rubber plug; had to replace the plug and all is well.
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