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While you may be tempted to add a little more gas to your car to round off your dollar sale- even at the risk of overfilling the tank-this is one instance when you shouldn't go with the flow.

Topping off the gas tank isn't just bad for the environment, according to the U.S. Environmental Protection Agency (EPA), it's also detrimental for your wallet. Because the gas nozzle automatically clicks off when your tank is full, topping off can result in your paying for gasoline that is fed back into the station's tanks via the pump's vapor-recovery system, which prevents gas vapors from escaping into the air and contributing to air pollution. In fact, topping off might even foul up the mechanism and cause not only a gas-pump failure, but also a potential air-pollution problem.

Plus, evaporation from the spillage of gas from overfilling-which you've paid for, by the way-contributes to bad-ozone days, is harmful to breathe, and is a source of toxic pollutants such as benzene.

You also need some wriggle room in your gas tank to allow the gasoline to expand, otherwise the additional gas could evaporate into your car's vapor-collection system and damage it, leading to a vehicle that runs poorly and has high gas emissions. ::EPA

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