black soot buildup on street from car
 

i started my 85 300D up today, and let it warm up for a few minutes. i gave it a little gas a few times; nothing over 2500 rpm. i noticed later that there was a bunch of soot (i guess that's what it is) on the street beneath where the tailpipe was. i only let it warm up for maybe 5 minutes...is this normal?

My 1985 300D does the same thing when I apply some pedal to get it out of the driveway... I have 'soot donuts'! I think it's normal but would like to hear what others say.

Mine turns the snow black when I start it :D Ash all over the place, especially if I give it a little revving from a cold start.

Mine doesn't leave any noticeable soot "stain" or anything on the driveway. I really get no smoke coming out of the exhaust at all. Of course I'm sure it depends on how old the car is, how the engine is holding up, etc... Mine doesn't have many km on it and it starts after about 2 seconds of cranking in -20 celsius overnight after 15 to 20 seconds of glow time (after the light goes out). Hopefully it will keep working so well! :D

The exhaust doesn't even have a diesel stink to it any more since I started using Sunoco Gold Diesel instead of whatever diesel I could find. It's only 2 or 3 cents more per litre and it doesn't smell at all. Seems to burn much cleaner and be more powerful. They do advertise it as having a higher cetane rating among other things, including cleaner burning. Seems to be great fuel. Anyone else tried Sunoco Gold Diesel?

Totally normal. All of mine do that. RT

ok, i feel better now. i thought something major was wrong

All 3 of my diesels have done that, and I never free-rev the engine when it's cold. The SDL makes nice spots on the wall of the parking garage at work, since the exhaust comes straight out the back instead of turning down. I've noticed that on all of them, a few little chunks get dislodged and come out of the pipe when you start the engine, especially if it's humid outside.

Perfectly normal.

I think there is more soot on the back of my car than on the driveway :D

My exhaust also points straight out the back since the muffler guy changed it. I think I am exempt from the smoke survey because well...I drive...spiritedly...

Hmmm... Strange, my SDL rear muffler has pipes that turn down at the end.
I too leave sooty spots when starting from cold.

Dataiv: I also use Sunoco Gold Diesel since I got the car home to Canada (from Texas) in August, so I don't really have any comparison with other fuels. I can't say there is no smoke or diesel smell, as there definitely is, so I don't think it is the fuel. Your car must be in particularly fine shape. :)

Diesels with the trap oxidizer don't seem to leave the soot marks.

I usually rev it upto 1500-2k rpm max (15 sec after oil pressure comes up) when cold because it seems to smooth out the idle quite a bit. Only after doing that I leave soot marks, no marks on a regular idle.

My CD doesn't leave black marks.. but it does make divits in the sand when I let it idle and don't move it.

Divots in the sand :D
 

My '84 300D (Fatmobile 3) leaves clear partches on the gravel hardstand where I park it. All of the gravel pebbles are moved away from the exhaust. No black marks, even on concrete driveways (couple of fuel/engine oil spots though).
Mrs's car (Josephine) has leak from Cam cover, so leaves many black spots - will replace gasket when I do valves next month.

I had the same question about three years ago when I first got my diesel, and noticed it happened when it was really cold out much more than when it was warm. The guys responded as it being the initial incomplete combustion b/c of lack of residual cylinder head temp to assist in getting the fuel burned completely.

Adamb has it right, this is normal as it takes a while for the engine to warm up and get complete (mostly) combustion. Also exhaust gases entering a cold exhaust system will tend to allow the water vapor to condense on the inside of the system and allow some of the soot to stick to the inside. As it warms up and dries out just a little bit of revving the engine will cause some chunks of soot to get blown out. There usually is a far amount of soot that can accumulate in the exhaust. If you have your car out on a dark hilly road at night sometimes you can see pieces of burning soot behind you when you floor it going up steep hills.