Brief puff of smoke while driving
 

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?

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.

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?

To measure timing chain stretch pull the valve cover and line up the engine at top dead center. Degrees of difference between camshaft stantion mark and crankshaft pulley indicate amount of stretch. They typically stretch out beyond 10 degrees at about 225k+ Miles (sorry dunno metric equivalent). If 6-8 degrees then IP timing reset will help compensate. Another option is offset woodruff key to re-align camshaft sprocket.

Routine maintenance should include IP timing adjust at/near 175k Miles, then timing chain replacement after another 60k or so. You will notice immediate performance upgrade also improved fuel economy.

My 1980 300SD needs timing chain replaced itself. Bought the car at 260k Miles and it smokes consistently - probly has 12 degrees chain stretch. In your case at 190k Miles I'd deffinitely set IP timing.

Excellent advice - I'll make this a weekend project when I have a little time to spare and the inclination to get a little dirty under the hood. I am loathe to touch the IP myself, but resetting the timing (or I suppose, solving the issue in an extreme way - replacing the chain) seems like something I might do in the new year.

On this timing issue....I would bump the IP toward the block (advance) just a skosh and see if that makes a difference. Be sure and mark the mating surfaces so you can move it back if theres no change. Remove the hard line nuts (17mm) at the injectors and bend them a little after you move the IP, not a big deal.