Fuel flows through all the pumps I know. 1/4 tank should ensure about
half the pump is in fuel.

"Ray O" <rokigawaATtristarassociatesDOTcom> wrote in message

The Ford pumps also have the fuel pass through the pumps to cool them.
However, even in this case chronically running the car with only a few
gallons in the tank can cause problems. Older cars (Ford, Toyota, GMs, etc.)
all had single speed pumps that were sized to provide excess fuel to the
engine under all conditions. There is a pressure regulator at the engine
with a return line back to the tank. Because you are circulating the excess
gas through the system back to the tank, the gas in the tank can get quite
warm, reducing its ability to cool the pump, particularly when driving on a
hot day at a slow speed in stop and go traffic, or if the vehicle spends a
lot of time idling. The more fuel in the tank, the bigger the heat sink, and
the less effect the recirculated gas has on the temperature of the gas in
the tank. But when you only have a few gallons in the tank, the fuel can get
very hot.

In recent years most companies are making the switch to variable speed fuel
pumps and returnless systems. These systems control the speed of the fuel
pump (and therefore the volume of fuel being delivered) in order to
eliminate the problem of "hot fuel." The variable speed pumps also require
less power on average.

Ed