Engine/Transmission (1998.5 - 2002) fuel line siphoning

[Ncostello]

Scenario: A person relocates the lift pump to the frame for various reasons. They install a shutoff valve before the pump (suction side) to make future pump changes fast and un-messy. So when (if) the pump gets removed, the shutoff ball valve prevents fuel from siphoning out the supply line coming from the tank.



But what about the other side? Is it possible for fuel to siphon through the return line... back to the VP44... and then backwards in the supply line? The check valve on the VP usually has a tiny air hole to release air but not allow full flow of the check valve.



Just curious if fuel can "backflow" through the return line, the VP and finally the supply line? I do know that the return does protrude down in the tank somewhat so there is a good chance the fuel is covering the return outlet inside the tank. Does this make sense?



I doubt the fuel would backflow through the cylinder head portion of the return line if it does reverse siphon at all. I'm more concerned with the return line portion that goes directly to the VP check valve.



I suppose anythings possible. Just thinking about what would happen if a reverse siphon scenario pulled unfiltered fuel into the supply line on the wrong side of the filter... as well as there still being a fuel flow to make a mess.

 

[illflem]

Yes the return will siphon back and be replaced with air at the high point, the injection pump. It happens very slowly though, you could change pumps without concern.

This airlocking is what causes hard starting after an overnight sit on a 12 valve with the infamous return line leak.