The problem with my 1974 240D continues and my mechanic and I don't know where to look next for an answer. The fuel system seems to be leaking air. The mechanic can get the car running and it can be driven around all day stopping and restarting without problems. After sitting overnight it will not start. Looking at the prefilter, I can see that it is only about 3/4 full of fuel. Using the hand primer and bleeding at the main fuel filter doesn't seem to help. I don't see any air bubbles coming out of the filter connection but the prefilter doesn't fill up.

The mechanic put on a new lift pump, drained the fuel tank and checked the tank filter, blew out the fuel lines with compressed air, checked the prefilter and main filter.

The glow plugs are OK. I live in FL and the temperature was 70 degrees this morning so its not a cold weather problem. How long do you have to pump the primer pump to work air out of the system?

Does anyone have a fresh idea about what to do?