Need car parts? Select your vehicle
Reading Time: 5 minutes
  • Drivers might be tempted to overfill their gas tank to avoid the hassle of going to the gas station, but it can be dangerous.Risks associated with overfilling your gas tank include your engine, developing performance issues, wasting money by pumping more gas, and harming the environment.
  • Overfilling the gas tank won’t damage the fuel level gauge, but it will trigger the check engine light if the Evaporative Emission Control (EVAP) system’s been damaged. The EVAP system uses activated charcoal to trap gasoline vapors. Its methods include vapor purging and computer-controlled purge.
  • Some fuel-saving hacks that you can try include traveling light, avoiding excessive idling, and coasting more.

Fuel is the lifeblood of any combustion engine一it’s what gets you from point A to point B.

And every driver knows two things: fuel can be quite an expensive necessity, and frequent trips to the gas station can be a hassle, which is why many overfill their tanks.

The Dangers of Overfilling the Gas Tank

For many drivers, overfilling the gas tank might be a nifty way to get the most out of their money at the pump. But in reality, it might do more harm than good for their vehicle, the environment, and even their wallet.

See also  How to Replace a Fuel Pump

Here are some of the dangers of overfilling the gas tank.

Risk of Developing Engine Performance Issues

Overfilling the gas tank can damage your vehicle’s evaporative emissions control (EVAP) system. This system traps volatile organic compounds (VOCs) or gasoline vapors and reroutes them to the engine instead of being released into the atmosphere.

car fuel tank overflowing with fuel
Overfilling the gas tank can damage your vehicle’s evaporative emissions control (EVAP) system.

The EVAP system handles gasoline vapors, not liquid gasoline. Overfilling the tank can clog the vapor intake hole with gasoline and eventually get sucked into the charcoal canister. Once this happens, the excess fuel can force a leak.

Every fuel tank has an upper volume chamber that expands whenever the fuel gets hot. It can hold between 10% and 20% of the tank’s volume. The chamber has a hose that’s vented to the charcoal canister.

A saturated charcoal canister can also result in an overly rich air-fuel mixture, which can cause the check engine light to illuminate. That can cause your vehicle to fail its emissions test, reduce fuel economy, and damage the catalytic converter.

Wasting More Money by Pumping More Gas

There’s a reason why you should stop pumping gas after hearing the first click.

Gas station fuel pumps have a vapor recovery system that can suck the gas from your tank if you overfill it.

The system has a thick rubber collar or accordion-like tube on the pump that covers the opening of the fuel filler neck. So squeezing every ounce of gasoline you can into your vehicle’s tank actually results in fuel waste, which also means you’re burning money.

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.

Harming the Environment Every Time Your Gas Tank Is Overfilled

Gasoline that spills onto the ground can seep into the soil and pollute water resources.

Air pollution is also a given every time gasoline is burned, and overfilling the tank contributes to this problem because of the gas vapors that escape into the atmosphere.

See also  Understanding Your Dashboard Gauges

Lastly, spilled gasoline is also a fire hazard, which can put you at risk of getting burned and suffering other injuries.

Frequently Asked Questions (FAQs) About Overfilling the Gas Tank

man taking a look at his car fuel tank
Squeezing every ounce of gasoline you can into your vehicle’s tank actually results in fuel waste, which also means you’re burning money.

Here are the answers to other questions people frequently ask about overfilling the gas tank.

Can Overfilling the Tank Damage the Fuel Level Gauge?

Putting too much fuel in the tank can damage the EVAP system, but it won’t do anything to the fuel level gauge.

Will an Overfilled Gas Tank Trigger the Check Engine Light?

Yes, especially when the EVAP system has already been damaged.

How Much Will It Cost to Repair a Damaged Evap System?

You can expect to pay anywhere between $200 to $560 to have a professional mechanic diagnose your vehicle, and the bill only goes higher from there when it comes to buying replacement parts.

In most cases, the mechanic will have to drop the fuel tank, which means you’ll have to pay more for labor.

In most cases, the mechanic will have to drop the fuel tank, which means you’ll have to pay more for labor.

Anthony Harlin, ASE Certified Master Automobile Technician

A Closer Look at the EVAP System

A typical evaporative emission control system has a fuel tank filler cap that has a pressure-vacuum relief valve. The valve opens every time the pressure or vacuum exceeds a certain value and closes once the pressure has been relieved.

The EVAP system uses activated charcoal to trap gasoline vapors because of its great surface area. Most charcoal canisters can hold either 300 or 625 grams of charcoal.

Fuel vapors adhere to the charcoal’s carbon surface because of adsorption. However, this attaching force is weak, so the EVAP system sends fresh airflow through the charcoal to purge the vapor molecules.

The EVAP system sends fresh air through the charcoal using two methods: vapor purging and computer-controlled purge.

See also  Lift Pumps: Function, Types, and Replacement Explained

Vapor Purging

Vapor purging is the process of mixing unburned gasoline vapors from the canister with the existing air-fuel charge.

Computer-Controlled Purge

Computer-controlled purge uses an electric vacuum solenoid and one or more purge valves.

Most engine control systems purge during closed-loop operation at cruising speeds. The powertrain control module (PCM) stops canister purging during open-loop mode, deceleration, and wide-open throttle conditions.

Fuel Saving Hacks

Overfilling the gas tank won’t help you save money at the pump, but here are some practices that will.

Observe Good Driving Habits

Slamming on the brakes and gas pedal, speeding, and screeching at corners make your vehicle consume more fuel. So drive carefully and avoid sudden acceleration as much as you can.

Travel Light

Carrying extra load means the engine has to exert more effort to move the vehicle. Lose unnecessary weight to improve your vehicle’s fuel economy.

Avoid Excessive Idling

Idling for extended periods can burn fuel fast. You might want to switch off your engine if you’re planning on staying at a parking lot for a couple of minutes.

Practice Coasting

Gliding into your stops is an efficient way to save fuel because it keeps your foot off the gas pedal, but your vehicle stays in motion until it slows down. It also prevents the brake pads from wearing out too quickly as a result of getting activated at high speeds.

Keep Tires Inflated Properly

Underinflated tires can decrease gas mileage. Make sure your tires are inflated according to the manufacturer’s recommendations. It’s also important to rotate the tires, so they wear out evenly.

About The Authors
Written By Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at

Tony Harlin is a Master Gas and Diesel Diagnostic Technician with over 18 years of experience. He works full-time at a large independent automotive shop as a driveability and repair technician working on all types of vehicles with a focus on diesels. ASE certifications include A1-A9, L1 and L2, as well as X1.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

File Under : Engine , DIY Tagged With : , ,
chemical guys
Notify of
Inline Feedbacks
View all comments

View all Questions & Answers

In the garage logo Newsletter Answers BE PART OF OUR COMMUNITY: Share your knowledge & help fellow drivers Join Now
Copyright ©2023, Inc. All Rights Reserved.