Yet another blue/grey smoke thread, W115 240D

[billhard]

I have been chasing a blue / grey smoke problem in my w115 1975 240D for a few months now on the vintage forum(this thread), thought maybe some fresh eyes here might help. I only get smoke when pulling away after the car has sat at idle like a stoplight, but it’s enough to see it buffet off the car behind me. Once moving the smoke clears or perhaps I can’t see it anymore. The engine pulls very strong although it is the only 240D I have driven. Compression is above 380psi in all cylinders and I believe at least part of the motor was recently rebuilt.

Here is what I have ALREADY tried:

1. Cam chain timing is correct, zero stretch.
2. IP timing is on.
3. Valves are in adjustment.
4. Valve stem seals have been replaced.
5. Vacuum pump is not leaking oil
6. Oil bath filter is clean and not over filled.
7. IP diaphragm has been replaced.
8. IP oil level is correct.
9. Injectors – recent tips, pop tested and calibrated.
10. Popet cam housing on back of IP was rebuilt and IP holds vacuum per FSM (See post 30 on the above linked thread for details, this is a pneumatically governed car unlike the w123’s)
11. Fuel has been replaced, both filters replaced.
12. Fuel additive used.
13. 1 QT ATF run through in last tank.
14. Crank case temporarily vented to atmosphere, no improvement.
15. No oil in coolant, level stay constant.

I considered stuck rings, but would I have great compression and still have stuck rings? The valve guides are the only other thing I can think of but I don’t relish the idea of having the head rebuilt.

Any thoughts?

[SD300]

i heard the oil ring can be not on purpose, so the oil didnt get properly scraped off the cyl wall.
Does it burn oil?
if yours pass smog test then what to worry.

Mines passed our famous www.aircarebc.ca
my 76 240d max allow is 30, I got 10ish.
My 84 300sd had 20 point same max allowable is 30.
So both are koshered to drive in greater vancouver bc.

[kerry]

I'd look into the role that the butterfly valve is playing. Is it possible to keep the butterfly valve open while idling not allowing the buildup of vacuum in the intake manifold and see if you get the same smoke when pulling away?

[SD300]

Originally Posted by kerry

I'd look into the role that the butterfly valve is playing. Is it possible to keep the butterfly valve open while idling not allowing the buildup of vacuum in the intake manifold and see if you get the same smoke when pulling away?

the butterfly valve controls the RPM, when vac drops the RPM increase!

similar to a gas engine car.

[billhard]

Originally Posted by kerry

I'd look into the role that the butterfly valve is playing. Is it possible to keep the butterfly valve open while idling not allowing the buildup of vacuum in the intake manifold and see if you get the same smoke when pulling away?

Thanks for the idea, unfortunately the short response is no that won't work, for the longer version I will quote forum member Govert who is far more knowledgeable on the 616.916 IP function than I am:

Originally Posted by Govert

The vacuum for the governor of the pump is not created by a vacuum behind the butterfly valve, but by a venturi under the butterfly valve. The valve controls the amount of air flowing through the venturi. Also an increase in the speed of the engine will increase the air flow through the venturi.

The vacuum works upon the membrane. The membrane connects to the rack, so more vacuum and the rack moves towards the stop position. There is also a spring inside the governor that pushes on the membrane and so, if there is no vacuum, the membrane moves the rack to the full load position.

The rod to the IP controls the auxiliary mechanical governor, i.e. the poppet cam. That steadies the rpm at idle and at low speeds, otherwise the engine would be "sawing".

[bipolardave]

My man, I think our cars could be twins.

I've only been a Benz owner for less than a year now. However, I'm beginning to think that stamping out smoke on these 616s is like trying to rid your yard comletely of dandelions - it's a fool's errand.

I've had my IP rebuilt, rolled in a new timing chain, and had the valve seals replaced all within the last 6 months. Injectors are also new and the valves were adjusted when the seals were replaced. Fuel filters and fuel lines are also new and all fluids are fresh. The only differences between mine and yours are that I have lower compression and I use perhaps a 1/2 quart of oil in 2,000 miles.

Despite this, I still have some smoke. There's a hint of whitish smoke on cold idle at start up and a bit of black smoke when I get on the throttle or climb steep hills.

I have another set of injectors that I had rebuilt and will install them in due course. I'll also rebuild the vacuum pump as a preventative measure. But after that, this game of "whack a mole" has to end.

There is one good thing to come from all this work, however. My engine sounds silky smooth. No knocking, no nailing, and no hicccups. The only underhood sounds you hear are the clickity click of fuel injectors popping and the combustion inside the engine. So long as this continues to be the case and my oil consumption doesn't increase, I should consider everything else to be inconsequential.

[billhard]

Originally Posted by SD300

i heard the oil ring can be not on purpose, so the oil didnt get properly scraped off the cyl wall.
Does it burn oil?

Yes it burns oil, at what rate I am currently measuring. My guess would be about 1 quart per 500 - 1000 miles. I guess this idea speaks to stuck rings, can anyone else chime in on this possibility? As I asked earlier can I have a stuck ring and not see a significant loss in compression?

Originally Posted by SD300

if yours pass smog test then what to worry.

There is no smog test here in California on diesels this age, at least not yet! As for why I care it's partly a self-conscience knee jerk, not wanting to look like the MB in the recent BMW diesel TV ads. You can only live amongst a huge number of tofu farting Prius driving Southern Californian environmentalists for so long without some rubbing off on you. Also I have worked hard on this sled and would like it to run correctly.

[billhard]

Originally Posted by bipolardave

Despite this, I still have some smoke. There's a hint of whitish smoke on cold idle at start up and a bit of black smoke when I get on the throttle or climb steep hills.

I could live with that and your right trying to rid this car of smoke is somewhat of a nutty obsession.

[bipolardave]

Originally Posted by billhard

I could live with that and your right trying to rid this car of smoke is somewhat of a nutty obsession.

I think we're both anal about our cars operating as we envison they should. However, my frame of reference is newer cars which, of course, don't smoke unless there's a failure of some sort.

I don't think it's a fair to compare our W115s to a new, just off the lot Bluetec. They weren't designed to the same non-poluting standards. Although I don't like to accept this as I want a smoke free car, facts stand in the way: our cars are what they are...occasional smokers. We just have to learn to accept their faults and live with it.

[SD300]

Originally Posted by SD300

i heard the oil ring can be not on purpose, so the oil didnt get properly scraped off the cyl wall.
Does it burn oil?
if yours pass smog test then what to worry.

Mines passed our famous www.aircarebc.ca
my 76 240d max allow is 30, I got 10ish.
My 84 300sd had 20 point same max allowable is 30.
So both are koshered to drive in greater vancouver bc.

My 300sd was pulled over by a cop for excessive smoking too, it did went thru the smog test.

So as the 240d , went to one centre, the manager clown told me my car is smoking too, he refused my testing, I added some Lucas fuel injector cleaners
it did reduced the smoke quite a bit.
Perhaps that may help.
Is only <$20 a bottle.
cheers

[SD300]

Just read Water injection will make them rings unstuck too.
If yours is non turbo then WI is pretty simple matter.
Find a water spray nozzle, go to these gardening /lawn spray places , should be able to buy these jets for real good price.er
Run a windshield water bottle with electric pump in it.

Few yrs back a guy has a bored out 440 super bee or charger, he mounted a water sprayer on top of his carb intake, wired to a micro switch on his gas pedal, it connects when partial throttle. This allows him to run lower octane gas for his high compression engine.
little do i know it will also reduce blowby too.
cheers