How much smoke is normal? '76 240D
 

So my other ride is a '76 W115 240D that I've had for a long time now, it truly converted me to the Benz way of life forever!

My main concern with this car has always been its tendancy to smoke. It has always smoked, and it hasn't gotten better or worse in the last 6 years. Actually, it gets a little smokier when I run B99, which is a tradeoff since the engine runs smoother so I compromise with a blend.

Now, this car has been around the block but I'm certain (and my mechanic mentioned this too some years back) that this car had an engine rebuild at some point. But I have no verification for this, only the fact that it has great compression, starts on the coldest mornings, and literally has never let me down, ever! This car has never stalled even except for twice when I ran out of gas!

Oil consumption seems fairly normal, I never keep meticulous records but when I think about it I'm sure I never go through more than 1-2 quarts per 3000k.

The smoke isn't horrible, a greyish smoke, but its enough that I don't feel great about driving it!

Oh, DEQ here was a breeze, the smoke wasn't a problem.

My mechanics mentioned that the older diesel Benz's tend to be smokier , that the fuel delivery system was changed in the mid 70's...........BUT......
I just bought a '72 220D and it doesn't smoke hardly at all, mostly just at startup. This has a fairly fresh engine but still.....

So, fell W115 240D owners, how much do you smoke? Should I feel bad about it? Anything to try? I did try some of the Lucas oil additive for awhile but this didn't seem to help much.......................

thanks!

mark in Portland

With the low sulfur diesel, it shouldn't smoke that much any more unless your're floored. If you're leaving a trail at steady speeds, something's not right.

You could start with a diesel fuel treatment. Stanadyne is excellent. See if that helps. If the car doesn't see much highway driving at speed, that'll make it smokey because things are getting all carboned up. Take it for a good 30min out and 30min back at speed, with Stanadyne onboard, and see what you think when you get back.

I wouldn't put anything in your oil, that's a waste of money.

Diesels need as much air as they can get, so make sure your air filter is really clean. The more the airflow is choked off, the more they are overfueled and smoke. Valve adjustment is critical too, because that's how they take in air, and exhaust their combustion gasses.

You might consider having the injection timing checked because if you're firing the injectors at the wrong time, that could make it smoke due to the inefficient burn.

Lastly, I don't know if there's an external fuel adjustment on your pump (there is on the VW Rabbit Diesel injection pumps), but if there is, you can adjust how much fuel is being delivered. On the Rabbits you can screw this adjustment "out" to lessen the amount of fuel delivered.....so you rev the engine and adjust the delivery so that you just start to get heavier black smoke only towards the end of a full throttle rev-up. But again, I don't know if your pump has this feature.

Of course you could also have a bad injection pump.

Those are just some ideas off the top of my head. Start with the symple stuff first, and work your way toward the possibility of having a bad pump.

I used to have a W123 240D which has essentially the same engine and it was virtually smoke-free, even at full throttle. I think the main thing is to have the valves adjusted properly and of course the injectors must be spraying right as well. Try an injector cleaner & cetane booster and if you have no record of the valves being adjusted, do it ASAP.

more
 

Well I can say that I've had the valves adjusted at least once a year for the last 5 years, and just had them adjusted maybe 2 months ago.

The shop where I take it said they couldn't do much about the timing.

The air filter is good and clean, its an oil bath and gets changed out every oil change.

Yeah this car has always smoked on startup, smoked when it warmed up, and leaves off smoke on acceleration during. Greyish smoke.

Could this just be worn rings, the engine burning oil?

mark

It's probably not burning all the diesel fuel that's being injected. If the compression is good, then it's either bad injectors or incorrect timing. How's the chain stretch?

our '75 was like that, still smoked even after all the other mentioned items were double checked. Reducing the full load about 3/8ths of a turn finally cleared it up for good. It's an external adjustment on these ones. Good luck.

Nether of my 123, 240Ds smoke except a little at start up. I'm guessing its not rings, valve stem seals or something linked to major ware. She starts when its cold, good compression, hopefully it will be a cheap and easy fix.

reducing full load?
 

So, how would I go about reducing full load? Is this done on the injection pump?


mark

I also am interested in this adjustment. I get a big plume of grayish smoke on startup (in the 115, the 123 doesn't smoke at all), and some smoke at idle. I don't notice much when I'm driving after its warmed up.

I also have to check the valves and the air filter I think it due, but after those things, I might try that adjustment. Did you notice any performance changes?

I dont think there is such an adjustment on his IP, that can be preformed by mere mortals. :(

Does your car have a Pneumatic or Mechanical Governor?
The Mercedes with pneumatic Governors have a Butterfly Valve in the Intake Manifold and a hose/tubing going from the Governor to the Intake Manifold.
Inside of the Pneumatic Governor is a Diaphragm made of oiled Goatskin (that is what I have been told). These Diaphragms get stiff as the bet older (they are also almost $200 each just for the part). There is some talk about them in the Vintage Mercedes section.
Also the Vacuum hose to the Governor and the port that is open to air in the Governor can become plugged or restricted over time.

You did not say how many miles are on your car or how many miles it has been since you had the Fuel Injectors Checked.

The Timing Chain stretch that the other member was talking about causes late/retarded Camshaft and Fuel Injection Pump timing.

Evidently your Mechanic does not know how to check the timing on your Fuel Injection Pump.

What about the vacuum pump? If the diaphragm is cracked it could be leaking oil, which is dumped into the intake, or is the 115, 240 different? Hows your vacuum?

I drove a 74 240D for many years. The greyish smoke is an indicator of a retarded timing, just a bit.
Too advanced will produce black smoke.
The smallest rotation of the pump will do the trick. You want to advance the timing
Easy to reach the lower pump nut with a long 1/4" extension
Remember to slack of the support bolt at the rear of the pump and make a score or punch mark to reference the original position. Just slack of the injector lines at the pump, no need to remove for this small adjustment. Don't let the pump element turn.

I second checking this, mine tore through and was like a fogger. Man were people PO'ed! :D

He seems to have disappeared,.... In a cloud of smoke :D:confused: