Originally Posted by brucemc
Regarding the fuel level to keep the pump cool, you do understand the fuel is being pumped THROUGH the motor, right? Yes, the pump picks up the fuel, sends it through the motor and on its way to the filter/engine.
There is some truth in what you say, but not in all applications. Fuel may be going "through" the pump, but it's passage is limited to the impeller, valves and associated passages. The heat generated by the electric motor driving the impeller is what we're concerned with, and that is absorbed by the motor's metal casing. For that heat to be sufficiently dispersed, it needs to be submerged in the fuel, which pulls the heat away much faster than still air.
I, therefore, belong to camp "Keep the tank 1/4 full or more"... if there is such a thing.