I have a 1995 Mercedes 300D that I have been running on biodiesel (B100). I recently had a leaky injector. My mechanic had to pull the head (and send it out to be check for a crack - there was none) to replace it. I drove over 600 miles after I got the car back and then experienced a run on condition; while driving on the highway the engine started to race and smoke belched out the exhaust. I slowed down and the condition passed. It happened a few miles later.

I took the car back to the shop and found that fuel had leaked into the motor oil and this had gotten into the combustion chamber(s) and caused the condition above. The mechanic claimed that the work he did was not related and would not have caused this. He suspected that either the injection pump was leaking or the lift pump.

He replaced the lift pump but I have not driven much so I don't know if the problem is solved, but I suspect that the mechanic will next suggest having the injection pump rebuilt, which may cost $2,500 or so, and I'm looking for advice on what might be the cause of this problem and how to solve it.

When we drained the motor oil there was about a gallon of fuel mixed into the 7 quarts that should have been there.

Thanks,
Jerry