This morning at the gas station, Daniel noticed two different pumps. One said gasoline. One said diesel.

He couldn't let it go.

Why do cars need different fuels? Isn't fuel just fuel? And what would actually happen if you put the wrong one in?

In this episode Daniel and Mom figure out the answer — and it turns out the difference between gasoline and diesel isn't just what they're made of. It's how completely differently they behave inside an engine.

Both fuels start from the same place — crude oil, the thick dark liquid pumped out of the ground. But they're separated during refining at different temperatures, which gives them different properties. Gasoline is lighter and evaporates quickly. Diesel is heavier and oilier, and has a little more energy packed into each drop.

But the really interesting part isn't the fuel ...