"Bill Putney" wrote in message news: snipped-for-privacy@mid.individual.net...
As I understand it this concern mostly applies to older systems that included a return line, not more modern systems that use returnless systems and variable delivery pumps. The concern is that continually running with low fuel levels can lead to the fuel temperatures becoming much hotter than desirable. Older systems with a return line pumped much more fuel than necessary to the engine compartment - particularly during low speed / low power operation. The excess fuel is diverted back to the pump at the pressure regulator under the hood through the return line. However, this process of pumping the fuel to the front of the car, through the hot engine compartment, and through the pressure regulator heats the fuel. With a full tank, the warmer fuel being returned to the tank only changes the overall temperature of the fuel in the tank slightly. However, when the tank is nearly empty, the hot fuel coming from the return line has a much greater effect on the average temperature of the fuel in the tank. Repeatedly running the tank with low fuel levels results in a much higher average fuel temperature, particularly in hot climates. Higher pump operating temperatures can shorten the life of the pump. I can't say how much hotter the fuel can get, or how much this can shorten the life of the pump, but I do understand the theory. I suspect it was much more of a problem 20 years ago than now. I know my Sister, a chronic low tank driver, had to replace two in-tank fuel pumps on her mid 80's car, but her late 90's car never had a problem.
And even if the fuel never get so hot so as to contribute to a pump failure directly, running around with very low fuel levels can lead to running out of fuel altogether, which is definitely not good for the fuel pump.
Here are some interesting references: