Is Hot Gasoline Costing You More?

One of the oldest and most -contested bits of advice for saving on gas is that by filling up your tank in the morning, when it’s cool, you’ll get more gas for your money.

The idea is that a gallon is a gallon is a gallon, but when you’re talking about gas, what’s inside that gallon is subject to change. The infinitesimally small molecules that make up a gallon of gas are tightly condensed when they’re cool. They expand when heated. That means a gallon of warm gas will contain fewer molecules than a gallon of cool gas.