I have a 1981 300sec with 159,000 miles on it. It now blows out blue smoke after letting off the gas going downhill and giving it gas at the bottom. I get a big puff of smoke then it stops. I get no smoke as I accelerate. Or travel at a fixed speed. I just had new valve seals put in because I was having little puffs smoked coming and a little oil consumption. After new valve seals I get more smoke and oil usage the ever. Can vale seals be put in wrong or what? Bad ring, Bad valves or valves guides ? What to do next?
Thanks PKBell

 

I'm betting it's the piston-rings

 

What kind of oil do you use?

 

Hi
I had same problem
I have a 1991 560 SEL , exactly as same as yr situation.changed the seals and problem was still there
I am not a technical person, but mechanic showed me the "TYPPETS" which seals are put around them ?? and they were very slightly bended.

Changed them ,got it brand new from germany and now the engine is same as new.dont loose oil at all.

Sorry for my technical ignorance

 

I would guess that the valve guides are worned out. New seals can not compensate for badly worned guides.

P.E.

 

It could be one of the seals were knicked when installed.

 

I am having nearly the same problem in my 1988 560SEC. The car runs extremely well except for an intermittent problem when going down a long steep hill and coming to a stop. After accelerating from the stop, the car hesitates and seems as if it might stall, but it produces a huge cloud of smoke (as in zero visibility behind the car, stopping traffic) as it burns off the oil getting sucked in.

The car is completely upto date on all service and has been gone over carefully. The timing chains are nearly new, and I was told the valve seals are in good condition. 125k miles on the engine.

Has anyone solved this problem? I know there is another thread from a French member who has this problem with his 500SEC.

 

The shop foreman at the MB dealer thinks that this problem is simply the transmission modulator, which makes the most sense to me based on the symptoms and the color/scent of the smoke. I will post updates.

 

I would look at the modulator prior to the valve seals, since the labor is much less on the modulator, and the smoke can eb similar in color.

Have you had a leak down or compression test done to ensure valve/ring condition?