Park uphill, no start
 

I have a 1987 300SDL. Sometimes when I park it overnight facing uphill. it seems like there's no fuel, and it won't start. I roll it backward and aim downhill. Then after some cranking, it comes to life (no smoking). Suspecting suction in the fuel tank, I drilled a small hole in the fuel cap (upon the advice of Mercedes mechanic). Problem still recurs, but only on a reasonably steep hill. Fuel is always visible in the fuel filter. Mechanic says maybe the fuel thermostat, which is upstream of the fuel pump. Expensive guessing game! Anyone had this happen?

dcalei

You do not have a good seal somewhere in your fuel system. How does it behave with a full tank of fuel?

I agree, the fuel is draining back to the tank so the engine is starved. A properly sealed fuel system would not allow this to happen.

I would check connections at all the fuel lines and filters in the engine compartment for starters. Carolton Hughes on this forum has a recent post about pressurizing his fuel system at the fuel cap with 5 psi. He found his air in the lines in the form of a leak fast.

Just curious, as another test could he just try priming with the pump to see if it replenishes positive pressure in the front leaning up position?? I ask because I'm learning ,too.:pirate:

His is self priming, it does not have a pump primer.