If you’re like me you never fill up your gas tank all the way, but even us half tankers have to fill it up all the way sometime, right? Well, then you know that when you fill up the tank the machine will automatically make a clicking noise when it is full, indicating that your tank is full. But what do we all do? We continue to fill up until it clicks off again to get a little bit more gas. But not so fun fact, that is not actually a good thing to do. 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 your gas tank isn’t just bad for the environment, in the case you spill, it is also bad for your wallet. Because the gas nozzle automatically clicks off when your tank is full, topping off can result in you paying for gas that is fed back into the stations’ tank 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.

Evaporation from spillage of gas that overflowed from you putting too much gas in your vehicle contributes to bad-ozone depletion and is harmful to breathe in. 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.

So next time you’re at the pump and you want to add just a little extra gas to that already full tank, do yourself and the environment a favor and don’t! It could save you money and a headache down the road!