On two occasions, I parked facing up on a friends hill (one month apart) and when I went to start the car (98 E300D) cranked but wouldn't start. I took off the fuel filter and it was half full so I filled it with diesel and the car started after cranking a bit.

I figure that the fuel drained back out of the filter, but there are no fuel leaks anywhere. This never happens when I park in my own driveway which is flat.

Is there a check valve or some other thing I should check. I know I can avoid the problem by parking front down hill, but would like to solve it correctly. I searched but couldn't find any clues.

Hope someone out there can help.

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1991 300D 172,000 (totaled)
1998 E300 Turbodiesel 82,500