How To Know If You Overfill Your Gas Tank? Tips to Know

Most drivers – especially beginners – often have the deadly assumption that the more gas filled in the tanks, the better.

Some even believe that overfilling gas tank is the best way to ensure the car always has enough fuel for operation! 

As someone who used to experience the disaster of overfilled gas tanks, we cannot stress enough how wrong that misbelief is.

This insightful article from Bryan’s Garage will instruct you to avoid such disasters by explaining how to know if you overfill your gas tank;

after all, it’s important to supply the car tanks with just the right amount of gas – no more, no less!  

What Happens If You Over Fill Gas Tank?

how to know if you overfill your gas tank
What Happen When Overfilling Gas Tank ?

In most cases, once the tanks start getting overfilled, you will notice the pump nozzle’s sudden automatic shut off, which implies it’s time to stop your tank filling.

And what if you stubbornly persist despite these warnings? Then the gasses will spill over the tank’s top and travel straight into the car’s filler neck, causing an overflow.

There will be two major problems at bay.

First, these extra fuels easily flood your car engine, coating the cylinder with excessive flows of gasoline.

We cannot even begin to tell you how that will become the death of your car – particularly older models. Many severe, irreversible issues might occur after that, including:

  • Spark plugs’ corrosion, which leads to the engine’s potential damage and misfiring accidents.
  • Air filter clogging that increases emissions and reduces the car’s airflow.
  • Gas film formations on the windshields. With a blurred and malfunctioning windshield, you will face immense trouble observing the road and navigating the vehicles to avoid accidents.

Secondly, overfilled gas tanks cause more fuel to expand, exerting extra pressure and force on the vehicle’s tank walls.

As a result, the tanks might inevitably rupture, leading to dangerous fuel leaks. Do not be surprised if the car stops working in the middle of the road! 

How To Know If You Overfill Your Gas Tank

How do you know if you overfilled your gas tank

There are several compartments you must check to assess whether the car tanks have been overfilled: the shut-off gas nozzle, the fuel gauge, the filler neck, and overflowing gasses (though this should be your last resort).

Let’s have a closer look at each one!

Fuel Gauges

One simple strategy is to observe the car’s fuel gauge and check where its needle points to.

Does the pointer reach beyond “E” or “F” (for full?) You have the answer right here: the gasses have far exceeded the recommended levels! 

Filler Necks

Another method is to check the automobile filler neck. Have you struggled to remove or bulge the cap? 

That might be a transparent indicator of the tanks being overfull. Plus, the dashboard or gas cap should also flash warning stickers to ask you to stop filling the tanks.

The Pump Nozzle

As mentioned briefly in the section above, some car models will have their pump nozzles shut off automatically if the gasses start to go beyond limits.

At this point, do not be stubborn and keep filling the tank; stop right there! 

Overflowing Gas

Nobody wants to encounter this tragedy, but that’s also a signal you might want to look out for if all the previous three indicators have escaped your notice for whatever reason.

If the gasses start overflowing to the ground, the car, or any nearby area, it’s time to stop the vehicle and fix the problem.

Extra Note: 

If you are not sure whether the tanks are overfull or not, we suggest taking caution and not starting the engine.

What To Do When You Overfill Your Gas Tank

overfilling the gas tank
What To Do if Your Gas Tank Filled

Of course, avoiding the accident in the first place will be the best scenario (which we will return to in later sections).

But suppose the tanks have already been overfilled; in this case, you should consider certain tips and tricks to minimize the possible damages.

Leave The Car Idle

This is among our favorite, all-time solutions: switch off the engines and let your car sit idle for several minutes. Such a trick is to let excess fuels drain back into the tanks.

The fuel caps must also get taken down. And on another note, you can use nozzle cut-offs to prevent the gasses from accumulating at the container’s top.

Handle The Charcoal Canister

Do you find extra liquid fuel on the filter canister of the tank breathers? Chances are the device will pull an error code and keep your engine from operating.

It means the canister must get replaced – but no problem, that could get done in a few minutes at an auto repair shop.

For older vehicles, experts recommend pouring water directly on the gasoline spills, which splashes them onto the floor.

Of course, some mopping and cleaning are required to scrub off the mess, but at least your car is no longer in danger.

Extract The Spark Plug

Another common troubleshooting method is to extract the spark plug from your car before using wire brushes to clean it off.

Why is it recommended? It’s because any gasoline spread onto the pin will be wiped out completely, protecting the car from further damage.

Still, to ensure 100% no technical issues, taking the vehicle to mechanics and having it checked by experts is a must. Professionals will inspect further problems (if any) and recommend necessary repairs.

Do Not Use The Car Immediately

Seasoned drivers always dread overfilled gas for a reason;

there’s a high possibility that the emissions control systems (placed on the fuel’s average maximum level) have been destroyed, which might cause flames or burning accidents.

Due to that reason, using the vehicles right away – even after you have already cleaned up the gasoline – is not discouraged.

It would be best to wait for some time (preferably 4-5 days) until the excessive fuel levels have returned to their normal state.

After that period, inspect whether there’s still lingering fuel and smell. If yes, you may have to pay more attention to the fuel tanks’ vapor canister.

Costly repairs are inevitable – but necessary for safe automobile operations in the future.

How To Prevent Overfilling The Gas Tank In The Future?

overfilling gas tank
What You Do To Prevent Overfilling The Gas Tank In The Future

Here are a few simple ways to keep these annoying accidents at bay.

Pay Attention To The Pump Nozzle

This small trick never gets old! Once you hear a thumping sound from the nozzle (a sound it often makes whenever the tanks are 100% full), remove the nozzle from the tanks and return it to the pump.

Any filling or transaction attempts will be stopped immediately, keeping the tank in safe territory.

Install Anti-Splash Valves

Some types of inlet hoses allow the installment of anti-splash valves to prevent the fuel from surging to the hose top after your tanks are filled.

Even better, it holds the liquid from touching any key components inside your car – such as the engine.

Install Overfill Prevention Devices

Want to take things even further? Then there’s no better way to do that than setting up overfill prevention devices inside the tanks themselves.

These products are often mounted onto the filler pipes, set to 97% filling (for underground tanks) and 95% (for aboveground tank fuses, a requirement stated in EN12285).

They work best for petroleum fuel liquids like leaded and lead-free gasoline, diesel fuel, and heating oil.

You can browse through different sizes and models to choose the one best fitted for your fill rate and fuel tank requirement.

Using them simultaneously with pump filling or gravity filling is also a terrific idea.


1. Can Overfilled Tanks Stall The Car?

Though such cases are not common, they can still happen, especially if you use bad gas or the liquid gasoline has already flowed to the recovery fuel vapor system.

Sometimes, stalled cars might also be put down to other factors. Click here for more info.

2. Will Overfilled Tanks Lead to Explosion?

Fortunately, no (although older cars might still witness flames and sparks). Exploding cars only happen in action movies! 


Bryan’s well-researched article has discussed how to know if you overfill your gas tank in detail.

We also provide a slew of tried-and-true methods to troubleshoot the problems and help you avoid this disaster in the future.

Keep in mind these guides to guarantee an efficient driving experience.

Most importantly, always double-check the car tanks at the end of every trip – so that whatever signals or problems there are can get on-time treatments without further delay.

The FAQ section, hopefully, has addressed some of your other major concerns; but in case you still struggle with gas tank overfill, our inbox is always open.

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