While some people don’t think too hard about how empty their fuel tank gets or about how much they fill their tank when they do fuel up, others are convinced that there is some magical fuel level that will keep the fuel pump running forever. Some swear by the quarter-full rule, while others say at least half a tank is needed at any given time. Is there a correct answer?

Why does the fuel level matter?

The fuel pump, which is responsible for getting fuel out of the tank, can generate heat when working for long periods of time. Most fuel pumps are designed to be cooled by the fuel in the tank acting as a sort of coolant. If there is not very much fuel, then the fuel pump can get hotter than it should, shortening its life.

As the fuel tank empties, air replaces the used fuel. Air usually has at least some water vapor in it and the combination of air and water will cause corrosion on the inside of metal gas tanks. The debris from that rust will settle at the bottom of the tank, and if the fuel tank is run dry the debris will end up in the fuel system. Most modern cars don’t have this problem, as they don’t use metal fuel tanks. Fuel still occasionally contains contaminants that settle to the bottom of the tank, and these can be stirred up and sucked up into the fuel pump if the tank is run low.

The optimal fuel level:

  • For short trips and regular commutes, keeping the gas tank at least half full is a good habit to get into. Getting it mostly full is ideal.

  • For longer trips, try to keep it above a quarter-tank and be aware of how far the average distance between gas stations is in the area you’re traveling through.

Keep in mind:

  • Fuel gauges are not always the best judge of fuel level. Try to get a feel for how your own vehicle uses fuel and how much you put in each time it says ¼ or ½ full.

  • A diesel engine can be damaged by completely running out of fuel.

This article originally appeared on YourMechanic.com as How Full Do I Need to Keep the Fuel Tank at Any Given Time? and was authored by Ian Swan.


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