Buying gas cold - Is it worth it?

There’s an internet meme that surfaces every now and then:

“It’s better to fill your car with gas in the morning, when the temperature is cold, rather than the afternoon, when it is warm. You get more gas that way.”

Image: Henri Bergius

Really? Is that true? Do you really get more gas when it is cold?

Because gasoline is a fluid, it is denser when it is cold*. Since we purchase gasoline by volume, there is real science behind this; there will be a difference in volume at different temperatures (after all, this is how hot air balloons work! Heat up air, and it becomes less dense than the surrounding colder air. If you trap this hotter air inside an envelope, through the principle of buoyancy, you can generate lift).

*Just about all fluids get denser when they get colder. There is a weird anomaly with water around 4°C, and it’s for this reason that pipes burst when they freeze, and life exists! But does it really make a measurable difference? If we take a gallon of gas at 80°F and cool it down to 20°F, what volume does it now occupy? I'd always assumed the difference would be trivial, and never bothered to research it further. However, just the other night, I looked into it. Here’s the jaw dropping conclusion:

It makes a huge difference!

(But there are a few caveats).

Science

Gasoline expands and contracts significantly with temperature changes; far more than water.

The magnitude of this volume change is measured by a coefficient of thermal expansion. This is often described by the Greek letter β. A thermal expansion coefficient measures the change in volume (as a ratio) based on a change in temperature. Below is a table for some common fluids. Typical units of this parameter are 10-6/K (how many millionths of the original volume does a fluid change with a change of one Kelvin).