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.

Worst case scenario: blown headgasket. Try immediately checkin the oil with engine running for water bubbles on the stick just after you start it when it's been sittin awhile, thats first thing I'd do.

If it is bluish white it may be unburnt diesel. leaking dribbling injectors.

It is normal for the temp to go up a bit on a hill.

Tom W

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Pull the injectors and have them pop tested. Inspect your prechambers whilst you are in there. Heatshields are a 1 time use but relatively cheap.

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Little do I know about diesels, but white smoke is usualy caused by burnt coolant if it has a sweetish exhaust smell or oil if the turbo seal went bad.

Thanks for all the replies and suggestions.

I just read "Why Does My Diesel Smoke? Diagnostic Guide" from **************. It mentioned that worn valve stem seals may cause symptom similar to mine. Just curious, how expensive will it cost to replace it on a W124 300D 2.5 Turbo?

I plan to take it to my mechanics next week with all the info I collected.

Thanks again.

The valve stems are not very easy to replace because the timing chain will have to be disturbed in the process. My imput on it is that if it does't burn a whole lotta oil leave it.
Turbo seals can leak oil into the exhaust, worn rings and valve seals.

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