Don’t Top Off in the Summer

The volume of fuel expands and contracts depending on the outside temperature. Summer is approaching, which means your fuel is likely to heat up. As the temperature of gas rises, the space it occupies increases. This expansion can lead to an overfill, causing the fuel to spill out of its container if it is filled to the top.

This concept comes from the Kinetic Theory of Gases, which states that gases are made of molecules that are constantly in motion and travel in straight lines until a collision with another molecule or wall of a container causes them to ricochet in a different direction. When the temperature rises, these molecules move faster, causing more, forceful collisions. This increase in energy heightens the volume, causing it to take up more space. According to Chevron, “the coefficient of thermal expansion for diesel fuel is 0.00046 per degree Fahrenheit. Using this value, 1.00 gallon of diesel fuel at 20°F will expand to 1.037 gallons at 100°F.” This can add up if you have a 100+ gallon fuel tank!

As a reminder, make sure not to “top off” when fueling if the container you are filling will not burn the fuel for several hours. Leave room in the tank for vapors to expand safely and prevent buildup of unwanted pressure. Overfill paired with heat leads to expansion and preventable spills. Give your fuel some room and don’t top off!

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