Does the gas tank overflow while filling despite not being full? These are the causes

It is not a rare occurrence to have a gas tank that is overflowing despite not being full when you are refueling your car. At the same time, it’s not surprising to see the fuel gauge reading half full or so regardless of the tank acting out in a manner that suggests it is overfilled.

Usually, it doesn’t necessarily mean that there’s a problem with your gauge though. A common cause would be an issue with your fuel filler neck.

Why Your gas Tank Is Overflowing Unexpectedly? Potential Causes

You may experience an overflowing gas tank mostly when the inner tube of your fuel filler neck comes off. Before explaining how to possibly fix it, here are a few facts about your filler neck that are worth knowing:

To begin with, your fuel filler neck is a metal tube that is welded to your car’s gas tank. At the end of this tube is what we call the fuel filler cap/gas cap.

It functions to prevent dirt, dust, and debris from going into your gas tank, basically providing a reliable seal and protection to your gas tank. However, you can take it out when you want to have more gas in your tank.

Notably, your fuel filler neck joins the fuel filler inlet and the rubber fuel fill hose on the gas tank. Moreover, there’s a steel hose clamp around the rubber fill hose that functions to seal the fuel filler neck, preventing any fuel leakage.

Over time, the fuel filler neck may rust and cause the fuel to start leaking from the tank. The rubber hose may also become weather-cracked, causing the same fuel problem.

All these issues can cause your gas tank to overflow when you are trying to fill it up with gas.

How To Stop Your gas Tank from Overflowing

Replace your filler neck if it is faulty. You can have your mechanic do that for you or do it on your own if you are handy enough. To that effect, here are the steps to do that:

  • Step 1: Park your car, making sure that the transmission is in 1st gear or Park mode, depending on your transmission type(1st gear for a manual transmission and Park mode for an automatic transmission car).
  • Step 2:Place wheel chocks around the front tires, engaging the parking brake to lock the rear tires from moving.
  • Step 3: Open the hood to disconnect your battery, taking the ground cable off of the battery’s negative post and disabling the power to the fuel pump.
  • Step 4: Raise the vehicle until the wheels are completely off the ground, using a floor jack.
  • Step 5: Place the jack stands under the car, making sure they go under the jacking point locations before lowering the car onto them. N/B: Follow the owner’s manual for proper jacking locations.
  • Step 6: Access the fuel filler neck by opening the fuel door.
  • Step 7: Remove the bolts or mounting screws attached to the cutaway.
  • Step 8: Remove the filler cap cable, placing it aside.
  • Step 9: Locate the fuel tank beneath the car, lowering it a little by loosening and removing its straps.
  • Step 10: Disconnect the harness, which is located somewhere on top of the fuel tank, from the connector.
  • Step 11: Further lower the fuel tank, making sure it reaches the vent hose to which it’s connected.
  • Step 12: Remove the vent hose and the clamp, allowing for more clearance.
  • Step 13: Twist and pull the fuel filler neck slowly out of the rubber hose.
  • Step 14: Install a new fuel filler neck and restore your fuel system.

N/B: A fuel filler neck is an Original Manufactured Equipment( OEM. As such, you want to buy a replacement filler neck strictly from the dealership where you did acquire your car.

Aftermarket alternatives may not fit into or mount correctly in your automobile. Using such products can cause significant damage to your fuel system.

Is It Safe To Drive With An Overfilled Gas Tank?

Gas topping is the overfilling of the gas tank with gas even though gas requires extra room to expand in the tank. This practice can have an impact not only on your car but also on your health and the environment generally.

Similarly, topping can cause the gas(liquid) to enter your car’s carbon filter or charcoal canister strictly designed for vapor. Not only can this problem damage the filter or canister, but also the engine in general.

This issue will affect your automobile’s performance and lifespan generally. It can also ruin its vapor collection system designed to manage fuel vapor and reduce harmful emissions.

Can The Check Engine Light Come On Because of This Problem?

The short answer is YES since the check engine light is designed to come on if there’s a problem with your car’s ignition, fuel, transmission, exhaust, or emissions systems.

Gas topping results in the presence of too much gas in the tank. As the gasoline expands, liquid gas gets into the emission system, which is not designed for the substance as explained above.

Consequently, the emission system detects a problem, prompting the check engine light to come on.


The gas tank overflowing problem above doesn’t often happen. But it can be a major issue if it does occur to you. Not only can it damage your car’s crucial components and reduce its lifespan significantly, but it can also put your health and that of your vehicle’s occupants at great risk.

More often than not, the main cause of this problem is a failing or bad fuel filler neck. Luckily, you can resolve it by replacing the filler neck with the help of your mechanic or on your own by following the simple procedure above.

Good luck with it. It saves time and effort to let a professional mechanic handle this process for you though.

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