Cars Simplified: Everything Automotive Explained

Fuel Caps

A fuel cap is a sealing cover on the fuel filler tube (which leads to the fuel tank) that allows the vehicle's tank to be refilled while keeping the fuel from evaporating out into the atmosphere at all other times. Many of them have internal vacuum relief valves that allows air in but not out, so the space that fills the tank as fuel is consumed can be filled with air, as opposed to becoming a vacuum that makes the fuel pump have to work harder.

Faulty Fuel Caps Video by Cars Simplified