Hello everyone! This is my first post to the forums after many readings. My friend Ron (Meltedpanda) pointed me here. He's also been helping me with my first Mercedes via email. I bought a '75 W115 200 in Indonesia that just died on the freeway a few days ago after exiting the freeway and coming to a stoplight. When I bought it, I replaced the condenser, distributor, rotor, and checked for a good spark. The electrical system is good. Typically it runs well, but it also runs like a car that is 35 years old. I've narrowed the problem to the PCV system coming into the carb and the intake manifold as the possible culprit as to why it died. It runs fine again, but I found some things out in the process of getting it running again. Here are all the symptoms:

Starts fine, idles a little rough at first. At start it blows some smoke and some black crud out the tailpipe (oil I assume), but then does not smoke at all after. Exhaust looks good except at start.

When some locals were helping me get it running again after it died, I noticed that when they pulled off the air intake from the carb it ran great, as soon as the intake was put back on it died. When I got it back to my garage and ran it, I noticed the same. So I did a search of the forums and the net and learned all about blowby and the PCV system. I always wondered what those little black hoses did... So I did a little more testing.

I did the "teakettle" test and the lid dances back and forth, but no shooting off, even when I plug the vent on the valve cover. The hose blows clean at startup, and then has a barely noticeable white smoke that smells more like gas when it warms up. It runs worst when the hose goes to the intake manifold and the carb (it almost dies), better when I remove the line to the carb (intake manifold hose still attached), and best when it is just blowing into the air.

Part of me thinks "emissions don't matter here anyways, it runs better without it, so just leave it off and run it" Another part of me thinks I ought to take notice because it indicates something else recently went wrong, is fouling the air in the crankcase, and is choking the engine through the PCV. Valve seals, a piston ring, etc. The blowby choking the engine is coming from somewhere.

What are your opinions? Must be repaired asap? Don't worry about it, leave the hose off and run the car? Time to sell it while it still runs well? Somewhere in between? I know that doing a compression and leakdown test would give me more info, but I don't know where/how to do that yet (just been here 8 months and don't know all the shops yet). Could I do those by myself?

Thanks for any help and opinions you can give!

Sounds more like a restricted air filter or air intake than anything else since you did not mention checking or replacing the air filter. That's a cheap and easy thing to check.

__________________
Erich Loepke
2010 Ford Focus
Currently Benz-less

Welcome to the Forum!

__________________

1962 220Sb ~ The Emerald Bullet http://www.youtube.com/watch?v=hx6tN1W48_o
1957 Ponton 220S
2001 S600 Daily Driver
The Universe is Abundant ~ Life is GOOD!http://www.classiccarclock.com

The smoke on start up is a sign of worn valve guides. When the car sits overnight a bit of oil trickels down the valve stems and past the worn guides and settles on the top of the pistons. When you start the car the oil on the top of the pistons burns away in a quick puff of smoke.

The amount of oil you are burning when the car is running is so slight you cannot see it. You only see it on start up because you are looking, if that is the correct term, at about a 12 hour accumilation of oil. A quick puff can result from a drop or two of oil on the top of each piston.

The blowby can be caused by a streached timeing chain or your valve timeing being off. A real Mercedes mechanic would need to look at this as adjusting valve timeing is somewhat beyond the scope of most new owners.

I would also recommend a compression check. Also, some of your trouble could be corrected by a simple valve clearance adjustment.

Thanks for the advice. I've been hearing about the valve adjustment and I have the instructions, so I'll try that and see how it goes.