It‘s important to understand why running the fuel low “can” lead to accelerated wear on a rotary vane type of fuel pump.
Fuel pumps don’t get their cooling from being immersed / submersed in gasoline, the cooling and lubrication comes from the fuel itself, otherwise they‘d start running hot as the tank comes off of full, most are mounted the same way our boats fuel pumps are mounted, from the top. On a lot of modern vehicles the fuel pumps are mounted on the frame rail outside of the gas tank, obviously these pumps, which are also vane style pumps, don’t need to be immersed in the fuel to stay cool. On our boats there is no fuel return line coming from the common rail on the engine where the injectors are attached, the fuel return is within the pump itself as is the regulator. The regulator allows the excess fuel / fuel pressure to go through a return line back to the tank, this occurs to some degree even at WOT.
As the fuel level reaches a low enough point where air can get into the fuel pump pick up, the fuel that then enters the vane portion of the pump where the high pressure is generated now has air in it that in turn reduces not only the lubricity of the fuel which generates heat and can produce scarring. The normal heat then cannot be hauled away from the pumps as well as the increased heat being generated by the aerated fuel. Remember, fuel, like oil, is a liquid and cannot be compressed, the crank, rods, bearings etc in your engine literally float or are suspended on a thin layer of pressurized oil, and that is how they keep from rubbing metal on metal. The same thing is happening in your fuel pumps, now put a bunch of air / gas which can be compressed into that fluid and the metal parts are no longer suspended from one another.
Keeping in mind that our fuel pumps with their pickup screens are mounted as low as possible in the fuel tank, primarily to have as much useable fuel as possible, ergo, as much liquid as possible can be extracted from the tank. The fuel pumps in the gas tank of my boat are located as far aft as possible, our boats run with a slightly bow high attitude and this keeps the fuel bias if you will at the rear of the tank. Or put another way, ensures the greatest amount of useable fuel from our tanks. As mentioned in my post above, I ran my tank down to 1% one time mainly to find out just how low the tank could go before the engines quit. As stated above the port engine quit while I was tied up to the dock, but started right up when it was on the trailer. It never hiccuped at all while underway. According to my owners manual, my tank is 52 gallons, and I put 51 gallons in it at the service station, pretty impressive really.
The fuel pump in my motorcycle is basically the same design as our boats and I’ve run my bike out of fuel numerous times, and ran low a lot of times and I‘ve not had a fuel pump failure associated with this. In fact I’ve not had a “pump” failure, what I have had is a fuel pressure regulator failure, stuck open at maximum bypass, caused by corrosion from ethanol laced fuel.
Do I advocate running around with a near empty gas tank? Absolutely not, that’s stupid but not fuel pump preservation stand point, from a reliability standpoint. On my diesel truck half tank is fill up time, unless I’m on a road trip then I may push that down to where the light comes on and I get the 50 miles to go warning, but I’ve also got two five gallon jugs of fuel in the bed. When I’m out riding, any time fuel is available the tank gets filled, that reliability thing. In my boat, it depends, but most of the time when I get fuel it takes 30 gallons, so that’s 40% left. BUT, I have no problem running the tank down to where the alarm goes off, I think that is 12% or 6 gallons remaining.
