Some background on the truck, the original owner had a 40 gallon tank installed into the bed by Transfer Flow, inc. They did a pretty good job of it and used a Pollak electric tank switch valve. Well that valve died a year ago, and just recently I got around to installing the manual Weatherhead valves that Bearkiller mentioned in another post. So I test it out, it works good, right. I didn't test it all, however. While driving I decide to feed from the main but return to the aux tank, 30 seconds later the engine dies.... crap. Hey at least the truck self primed and restarted when feeding from the aux. I thought I had an air leak in the main circuit and spent some time looking things over, it seems that the only time this happens is if I feed from the main and return to the aux. More research led me to a sort of answer, the main tank feeds from the mini reservoir in the pickup assembly which is where the fuel return dumps into. So ok, maybe its not designed to run without the return. I also installed one of those clear plastic fuel filters into the supply line as Bearkiller advised. So when feeding from the aux tank the filter is full, when feeding from the main the filter is kinda empty. I'm going to blame a plugged pickup screen in the main tank, and will post back with what I find. Just thought I would share some of this oddity here.

 

You probably hit the nail on the head about the stock draw unit sort of sucking from a sump that the return is supposed to always keep full.

When you switch the return flow to a different tank, the sump gets pumped dry and you "run out of fuel" although plenty of fuel is available.

I have much less problems from simple "line to the bottom" fuel draw assemblies.


On a similar note, I have discovered that should my engine run itself out of fuel for whatever reason, usually when I neglect to switch tanks or whatever, I can flip ON my stand-by electric-pump for a second and the engine will fire almost as quick as usual; that little benefit alone is reason enough to install one.