Hi all,

So, I have been watching this carefully, and am wondering whether I ought to be concerned. Here's what I observe:

I have a 1984 300D Turbo (123.123 with 617.952 motor). When the engine is warmed up and at operating temperature (coolant anywhere from 80-90 degrees C) I can drive around town in "S" and get a very tiny puff of smoke on starting from a full stop, and can also occasionally see a larger puff of smoke when I hit about 2500 rpm in 3rd gear, if I am accelerating moderately hard. I most recently observed this on an extensive (about an hour) drive around town and the behaviour was very predictable. Once I see the initial puff of smoke, it stops quickly (that is, I don't trail a plume of constant smoke or anything like that)

With the motor cold, or warmed up, I can rev the motor in neutral and I eventually will get black smoke, but not until I hit about 4500 rpm or more. I never see smoke with the motor idling. Blowby on my motor is very minimal - hardly enough to even move my oil cap if I loosen it. Overall, the car feels smooth and really strong, so I suspect I shouldn't be concerned. It might be worth noting that I haven't replace the air filter and do not know when it was last done. Maybe this is a likely culprit?

Also, I was driving around on the freeway in 3rd, pushing the motor up to about 3500-4000 (and driving in that range constantly) and couldn't tell if there was smoke (no streetlamps or following cars tonight) but I did notice after a few minutes that I could detect a distinct "exhaust" smell. Not sure what to make of that.

Lastly, I had some time ago asked about realistic fuel economy, and I am getting about 22mpg in town, after just having filled up and noted my distance travelled and fuel consumed. Not bad for lots of very short drives in cold weather.

Fiiiiiinally, I got my 250,000km badge from Mercedes-Benz, and boy! It looks lovely on my grille! Yay!

Thanks for any advice/reassurance!

hi xdjio - my wife's family is from Vancouver (well nearby anyway!)

Do you see the smoke in the day or only at night?
What color is it?

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

Oh nice! It's a great place to live. Please tell your relatives I also say hi, heh.

It's very hard for me to tell the colour of the smoke. The black smoke I talk about of course really is black - I can tell becuase I can produce it easily in my (well-lit) parking garage.

As for the smoke I see while driving - it's easiest for me to detect it at night because I can observe it in the headlights of cars behind me. During the day this is not easy. I can observe it during the day as well - chiefly in the morning when I drive my wife into work. It's not white smoke, more of a medium grey. Fairly insubstantial (not a dense cloud) but enough to notice.

I wonder how meaningful it is to note that after extremely short drives, when I park the car and get out, I can detect a real diesel exhaust smell. After long drives when the car has been thoroughly warmed up, I cannot detect it and exiting the car after I park.

over fueling... black is unburnt fuel

why do you drive in S?

I generally drive in S on my morning commute because I have a pretty hilly route, and I find it a bit easier to deal with all the various ups and downs in S. Correct me though, if I am mistaken in assuming this should do no harm (I've only been really doing that for about 4 or 5 days).

you're fine as long as you shift into D when the revs get a little high

what is the altitude in your area.. you mentioned hills.. perhaps a high altitude?

I know my diesel makes a good "fog" at night if I mash the go pedal

Both the smoke and fuel mileage you've described sound perfectly normal.

Interesting to know indeed. I have no real intention of staying in S when the revs high - this was more an experiment I decided to do since I had a lot of empty road at my disposal. Highway driving, I would always be in D.

Of course, now the curious part of me wants to know "why" this should be, unless I have already surmised correctly that it's just endemic to the normal functioning of the engine and injector pump (like why I can generate black smoke at high rpm).

As far as altitude? Very low altitude indeed - Vancouver's a hilly city, but generally all within about 100ft of sea level.

craig - thanks! that is good to hear. I felt confident that my fuel economy was spot-on, but was less certain about the smoke. What can I say, I'm still getting used to owning a diesel!

zeke - you may be interested to know that I am half-planning a road trip to the southwest one of these days. I can't wait to take the car on it's first big trip (as mine - prev owner took a number of large roadtrips to Florida in it and had nothing but praise for it)

Black smoke at high rpm is normal it's unburned fuel.

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I'm thinkin at mileage you've racked on original(?) timing chain, its probly due for injector pump timing to compensate couple degrees chain stretch. Roughly 2 hrs work if professionally done. Smoke is typical symptom of needing IP timing at/near 250k kilometers..... 150k miles?

Check your Air, & fuel filters. Keeping them clean makes a great difference in performance.

Will do! I'll check and replace my air filter for sure.

That's interesting about IP timing. Yes, I am on my original timing chain, and I have about 307,000km now (so, about 190,000 miles). Is there any accepted interval or metric for when the chain should be replaced?