My '85 300CD began to have cold start problems a few months ago. Missing and smoking. Then glow plug light would not come on at all and I rightly figured that was the problem. Bought five plugs but only did first four before daylight ran out. That made glow plug light come on and car started better but still had a little fit when cold. I began to think I had air getting into fuel line somewhere.

I put off doing last plug (near firewall) because I have read several times that the number 1 glow plug could be cause of problem and thought that four out of five (including number 1)should do the trick.

Finally got last one replaced last week and that completely fixed my cold start problems. No missing and no smoke to speak of.

I don't know about other 300's but mine wanted ALL the glow plugs replaced before being happy. Number 5 was causing big trouble. I assume the numbering is 1 to 5 from front of engine.

Nic
Columbia, SC