noob question: smoke = blowby?
 

Sorry for the noob question, but my '77 240d is my first experience with diesels.

I am trying to discern what to do, if anything, about the smoke the car produces at idle and at hard acceleration. I know smoke is endemic to older diesels, but what I am seeing is a touch on the excessive if excessive means that I am uncomfortable with what I am seeing when I sit at a stoplight. It isn't oil smoke, just plain ol smoke like my car is smoking a big stogie. The car runs pretty good otherwise.

I've done some searching around but am wondering if the term 'blowby' that is often used means the same thing as 'smoke coming out of the tailpipe' (and sometimes from the general area of the engine compartment).

And if you are feeling really generous, maybe you could point me to some good threads on troubleshooting smoke?

thanks.

Blow-by is the expanding gases of combustion that make it past the piston rings. To measure blow-by, simply open the oil filler cap whilst the engine is idling and place it on the opening without latching it. If the cap just rattles around on the opening, you don't have to worry. If the cap is blown off, you've probably got low compression in one or more of your cylinders. As for smoke from the tailpipe, (which I assume is black- which is unburnt fuel- soot), try adjusting the valves and/or the injection timing.

Blow by?
 

There is an internal diaphram to be checked out. Peter Hedary suspected that on my old '76 240, and after replacing it, problem gone. Check with him about replacing it. Later models did away with that system.

^^yes, I believe that diaphram is in the IP. But I don't think the W123's had this.

If you live in central FL and need a good honest mechanic with more than reasonable prices give Pierre Hedary a call, 407-765-2867. He only services Mercedes older than 1993.

If he has a pneumatic Governor it could be the Diaphragm. However, a new Diaphragm cost about $280 so it pays to look into other issues like Valves needing adjustment, poor compression or Injectors needing to be rebuilt first as a new IP Governor or IP timing; Diaphragm will not cure either of those.

If you think your Piston Rings might be sticking some take a look at this thread:
http://www.peachparts.com/shopforum/diesel-discussion/258757-compression-test-how-low-low.html?highlight=Marvel

I did the above to my car that had continious hazy gray smoke and it cured it.

Yesterday I did the diesel purge procedure using the lubro moly product and it so far seems to have made a noticable difference. Changed the fuel filters too.

It still is putting out some black smoke, which I assume is fuel mixture related. Can someone suggest the first place to check in regards to black exhaust output?

thanks!

Black smoke is unburned fuel and is a symptom of a dirty air filter. Change the air filter.

This may be irrelevant, but I had excessive white smoke and a lot of black smoke coming from my 300CD (1983), a simple valve adjustment fixed everything. Valve adjustment makes a worlds difference I'd do one, and on the 240 it's a breeze. Just make sure you get a new valve cover gasget unlike me.. :)