90 300SEL Overheated, No Compression
 

Need some serious help. My 1990 300SEL M103 Engine has been through hell while my younger sister was driving it. Anyway she was on the highway when she lost engine power. There was smoke and temp gauge was high. After car was towed home I inspected it. Removed spark plugs and found water/oil in all cylinders, engine does turns over, 2 cylinders have 25 psi compression and others have Zero.

I have 2 options, 1. Replace head gasket, get a valve job or 2. Buy a used engine.

Please, I need some help.

Based on what I've read, I'm assuming the head gasket is blown. If so, you now have coolant in places it should not be to include the lower area of the motor. The crankshaft bearings may have been damaged by the coolant being introduced into the oil.

From my way of thinking, it's more than just changing out a head gasket. The bottom end will need analysis and the entire motor will need to be cleaned to remove the coolant. In the end you could be looking at rebuilding top and bottom.

I'm personally leary of used engines. Just how used and what is already wrong or about to go wrong with it.

My 2 cents.

I would agree with Mike regarding used engines. I assume this MBZ has some miles on the clock, I would do at the minimum, a complete valve job, not just replace the head gasket. Your are lucky it is not a V-8

I would have a good mechanic check out the bottom end too. Under normal conditions the blocks will last for a long time. (Unlike cast iron), aluminum does not tolerate overheating. Not to mention the possible bearing damage. Best of luck. (Don't loan your sister any more of your cars!!)

I have an 89 with a fantastic engine (fresh valve job, chain bla..bla) however the the trans is bad and it needs paint. If you are interested in the car I'll let it go for a real good price..let me know.
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