Overfilling your gas tank can have several negative consequences, including environmental damage, safety hazards, and damage to your vehicles evaporative emissions control system. Here are some of the potential consequences of overfilling your gas tank:

• Environmental damage: When gas spills onto the ground, it can seep into the soil and pollute water sources. Gas vapors can also enter the air, leading to air pollution. When gas fumes are exposed to heat or sparks, they can ignite, leading to a potential fire or explosion.

• Safety hazards: When gas overflows from the tank, it can get into the vehicles interior, leading to a potential fire or explosion. This is especially true if the vehicle is equipped with an electric starter. Gasoline that spills onto the ground can also be a fire hazard.

• Damage to your vehicles evaporative emissions control system: Overfilling your gas tank can cover the vapor intake hole with liquid gas, which can then be sucked into the charcoal canister. This can damage the canister and possibly other parts of the system, which will cause the cars check-engine light to come on and could potentially cost hundreds of dollars to repair.

• Wasting money: When you force-fill, excess either flows out into a little drain below your fuel filler neck and onto your shoes, or it flows back into the gas pump in which case youre paying the gas station to take some of its own gas back.

• Engine performance issues: Overfilling the gas tank can damage your vehicles evaporative emissions control (EVAP) system, which can lead to engine performance issues. Certain engine components are also at risk of getting damaged every time you overfill the tank, so you can expect to pay a significant sum to fix them.

To avoid these negative consequences, its important to always be mindful of the level of your tank and to stop filling when its at the recommended level.