Originally Posted by Ski in NC
I don't think all Fords/Lehmans are plumbed the same. Last one I had in my shop for a rebuild I bench ran it and if I remember right it had a fair amount of return flow.
It's normal practice in the diesel world to have a drilled orifice or pressure control valve from injector pump to return. If you don't have that, it will not naturally purge air and can lead to stalling. On other engines like that (Yanmar GM) I have custom made a bleed rig to the return to get rid of the air problem.
Can't speak for the Sp120, but for my SP135 it returns a significant amount of fuel. I've heard it's about 10x the amount it acutally uses and this seems correct to me.
My return lines go to a "T" and then another "T" at the top of each tank at the top of the sight tube.
Thus if I have the top of the sight tube open, fuel will fill the sight tube in less than 10 seconds. I keep that valve (top of sight tube) closed for that reason when underway as I want the fuel to return to the tank.
This aids significantly in keeping cool fuel going to the engine and aids filtering of the entire tank.
I keep the return of the tank I am feeding from open and the other tank closed. Otherwise, when i have had both open, it did empty one tank in the course of a day (maybe 100 gal) and then the engine died
Evidently, using these returns was the way the previous owners transferred fuel. One of my goals when i added the Fuel Polisher system was to be able to transfer fuel quickly.