|
I'm in the same approx camp as wiredgeorge. We have a 90 gal aux tank and a 48 gal truck tank. If I leave the aux tank valve open, the truck tank fills to the top but doesn't seem to overfill - the fill cap is not vented as notanlines pointed out. However, if the truck tank is totally full, the aux tank drain valve is closed, the truck is just sitting, and the daily temperature gets very hot (say 110°F), the system will build pressure from the heated fuel in the full truck tank and begin to "drip". I have always attributed this to fuel expansion in the system with no place for the pressure to vent other than out of the system.
This never happened before installing the aux tank because it just was not possible to completely fill the truck tank and fill lines all the way to the cap using normal fuelling procedures. Once the aux tank was added, it drains into the fuel fill line and it becomes possible to completely top this system off with fuel.
Once I had this experience, I started either leaving the aux drain valve open (so that pressure could push back into the aux tank) or closing the aux tank valve and making sure that the truck tank was not totally full. This gives the pressure some place/way to vent.
Not sure if that is exactly what happens, but it seems to work for me.
|