Too much gas damages your car! Overfilling at the pump comes with some consequences. Your vehicle’s system utilizes gasoline vapors. Overfilling your tank can cause liquid gasoline to enter places only the gasoline vapors should go. The liquid can get sucked into the intake valve and end up in the vehicle’s charcoal canister or carbon filter (depending on the vehicle type). If this happens, the vehicle will start to run poorly and gas could start leaking into, and damage other parts of your vehicle’s system. If your charcoal canister or carbon filter needs to be replaced, it’s not an inexpensive repair, but ignoring the necessary repair could result in even further damage.