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When you open the fuel bay door on any vehicle, the gas cap is readily apparent. It is the physical seal that keeps gasoline inside your cars tank and the environment out. The gas cap performs three functions: improving safety, increasing fuel economy and reducing emissions.
Safety
Gasoline is highly volatile, meaning liquid gasoline vaporizes into a gas readily at room temperature. Since gas vaporizes easily, if your tank was not closed by a tight cap, highly flammable gasoline vapor would constantly leak from your tank.
Emissions
Gasoline normally burns cleanly within a vehicles engine. If gasoline vapor was to escape without being burned, it would damage the atmosphere like many other volatile hydrocarbons. The gas cap prevents leakage of atmosphere-depleting vapors.
Fuel Economy
For every gallon of gasoline vapor that escapes from an open tank, a gallon of usable fuel is wasted. Gas caps make sure the gas you pay for at the pump actually reaches your engine.
