While fuel pumps will run with low fuel, it also increases the chances of overheating and it will wear out sooner than normal. Fuel pumps depend on the fuel they are pumping to provide both cooling and lubrication. If the tank is below a quarter, the pump will be cycling air which reduces cooling efficiency and fuel temperatures can raise 20-30°F. With high-performance fuel pumps that function at a higher pressure, this rise in temperature will lead to overheating of internal components such as the impeller and seals and can reduce pump life by as much as 40%.
Filling up the tank means that there’s less work for the fuel pump to do, and it lowers the chance of the pump sucking up sediment from the bottom of the tank, too. Small debris gradually accumulates in the bottom of the fuel tank. These particles can enter the pump when running on low fuel and cause clogs, which inhibit functionality. Automotive studies show that clogs can reduce fuel flow by as much as 25%, leading to engine strain and reduced performance, which is particularly noticeable when accelerating or under load.
Older vehicles are at an even greater risk of damage to their fuel pumps, since wear-and-tear has reduced their ability to cope with high temperatures and contaminants. So mechanics typically suggest keeping the tank at a half tank or more is going to enable the pump to last longer in these cases. In fact, a survey of mechanics found that 60% of respondents advise keeping the fuel level above a quarter tank to avoid damaging a fuel pump and ensuring reliable operation since low-fuel operation can lead to wear that will require a costly replacement with an average cost of $200-$500 depending on make and model.
Even though modern pumps are designed by companies such as Bosch and Delphi to withstand short-term low fuel levels, they suffer from long-term exposure to hot and dirty fuel. Running for prolonged periods of time with little gas can affect the ability of the Fuel Pump to maintain adequate pressure in high demand situations, compromising the efficiency and longevity of your engine. Well, keeping the fuel levels well ensures the pump has less work to do, and therefore lowers the chances of messing up the pump which also reduces the need for repair costs.