I have a W124 1992 Mercedes 300D 2.5 Turbo with 240K miles. It has some smoke problem that I wonder if anyone can help me? I searched the forum but did not find any post matching my exact symptom.

When I start up the car, it often (not always) gave out a puff of white smoke (not vapor. Smell a kind of burnt). When driving for the first few miles, there is no smoke if RPM is below 1500. But once engine go over 1500 RPM, I can see white smoke. This will keep going for a few miles, then it got cleared up and no more smoke.

From what I read from the forum, white smoke is often unburnt diesel, and it usually happens when engine is cold, or during hard acceleration. However in my case, the white smoke will occur as long as the car has been parked for some time, regardless if the engine remains warm. I still need to drive a few miles to get rid of the white smoke.

I have tried two types of diesel additive (Run-rite and Diesel Kleen), and that did not seems to help. The car runs fine otherwise. I just took the car for a 2500 miles trip from California to Nevada to Arizona and back, and it runs like a champ. The only thing I noticed during the trip is when going uphill at 65 mph, the termperature rises to 110 F. But on flat ground at 75 mph, the engine temperature is between 80 and 90 F.

I really appreciate any comments/suggestions.

Thanks.