Questions and Answers

Mercedes Benz 300D Blowing Smoke Q. A friend of a friend has a 1983 Mercedes Benz 300D that he has offered to sell me for $2500.00. I haven't seen the car yet but he says it is in great condition but has 270,000 miles. He says it has a little smoke upon acceleration. I read where you said that a properly functioning Mercedes Benz diesel should not smoke. Should I consider buying this car? Would a cylinder compression check be a good idea? Thanks, Mark

A. It all depends on the color of the smoke Mark. If it is black, then it is possible the injection timing is off or there is a problem with the injector nozzle(s).

If it is blue smoke, that could indicate bad valve seals or piston rings. Yes, a compression test would be the way to determine which. A compression test on a diesel is a little more difficult because there aren't any spark plug holes to connect the compression gauge. So if you have it done, expect to pay more for the test.

Normal compression is between 345 to 435 psi with an allowable difference between cylinders of 40 psi. The minimum compression should be no less than 260 psi.

If the smoke is white in color, you are probably looking at a head gasket starting to go.