When you're filling up your car at the gas station, the pump knows when to stop automatically thanks to a clever mechanism.

When you fill your tank with gas, it displaces the air that’s in the tank. “The more gas goes in, the more air must come out,” McKenzie says.

The full-service pump at your local gas station is always a tempting option, particularly on cold mornings. Unfortunately, having to tip the attendant usually means most of us always opt for self ...