Bought my 9th Mercedes, but made a classic mistake. Been kicking myself as I of all people should know better, didnt check compression. But whats done is done, pity party is over, time to move on.

Number 3 cylinder has almost zero compression, only about 20 psi. Oil does nothing. With both valves closed I can blow on the test adapter and easily blow air into the cylinder without restriction and can hear it in the crankcase, so I know there is something very wrong with the piston.

The question now is, what to do with it? The car is real clean, most everything works, it drives really good, transmission is tight, overall its a very good car. But the mileage stopped at 117K, and it appears that was quite a while ago, so mileage is unknown. My gut says dump the car or part it out. Right now the car runs and drives, someone could drive it home a very long ways, or at least drive it to test the transmission. Once I pull the head, if I find something nasty, its all over.

OTOH, I could get lucky and find its just a bad piston. I wouldnt be opposed to putting one piston in it and drive the wheels off the car. Yeah I know how to do the job right, replace everything, rebuild the head, yada yada. But these things are a dime a dozen now, and its just throwing money away. I could buy another one of these for what it would cost to fix this one "properly".

But just a piston and headgasket, sump gasket, that would be cheap. And God knows, I'm cheap.

Opinions?

Do a half ass job and drive it till the wheels fall off.

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97 W202

Thats kind of what im planning, if theres anything left.

Seconded. Post pictures please.

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Prost!

I would use a borescope to look inside the cylinder before I pulled the head.
If you don't have one go to a shop that has.
Don't buy a cheap camera scope, they are useless for this kind of work.

Pistons only get holes if there is something wrong, like not enough fuel in that cylinder. You have to fix that.

Rob

If the shops which had a scope didnt want $100 to look, maybe. I guess the only real fear is if it dropped a valve, but the fact its making some compression kind of rules that out.

Ideally I would prefer to just sell the car the way it sits and wash my hands of it. I have enough trouble at the moment without opening another can of worms.

An update.

Its been sitting out back all this time. No one ever wanted enough parts off it to make it worthwhile to strip out, and no one wanted to buy it for more than peanuts. But it ran and drove (sorta) so I just left it alone. A few months back I saw another 300E sitting behind a mechanics shop, and long story short ended up running a compression test on it. 3 and 4 showed only 90 psi. That and that the car had sat 5 years and had no coolant in it, I walked away.

A week ago I went to look at another one being sold cheap, hoping to find a good motor. More low reading cylinders but this time I noticed vapor escaping from down in the plug hole. I wasnt getting a good seal. Was I condemning good engines with faulty tools? That car had other serious problems over and above poor compression so I walked away.

I finally decided to just pull the head and see. Nothing to lose, right? First thing I noticed was the #3 exhaust gasket was blown out on the bottom side. No biggie, just a notation. I pulled the intake, figuring if I was going to pull the oil pan to pull the piston it may as well be out of the way. So off comes the head and the piston looks perfect? What???? And its a burned exhaust valve??

I scratched my head a bit, while accepting the good news. I guess the air I was hearing was coming from the blown exhaust gasket, not the crankcase.

As we get older and more experienced, all too often we become complacent and assume things, based on our experience, rather than always being inquisitive like we are when we are young.

Im taking the head into town today and am ordering the parts to put it back together. Gotta lot of cleanin and scrubbin and some paintin of parts to do. Heck, I could be driving it by the end of the week. And were eatin crow for dinner.