There is a common belief that filling up your gas tank in the cool morning air will get you more fuel. The theory is that gasoline is denser when it is cold, so you get more liquid per dollar before the heat of the day arrives. While it is true that gasoline expands when it gets warm, the actual difference you see at the pump is usually quite small. Most gas storage tanks are located underground, where the temperature stays relatively stable throughout the day. Even so, there are still some good reasons to get your errands done early during a heatwave.
