Gas Tank Overflowing When Not Full—What To Do?

While on a long drive, you may have noticed that your gas tank is overflowing even though it's not full. Now you're a bit anxious as you still don't know how to deal with this problem. Luckily, we did some research for you, and here's what we found.

If your gas tank starts overflowing when it's not even full, it means the inner tube of the fuel filler neck may have detached from the neck. If you start noticing this problem, you should remove the filler neck so you can find out if the tube was knocked off. 

Vehicle owners usually face this problem when filling up their gas tanks. If this happens, it is important to know what steps to take in order to avoid any potential risks that may occur. Continue reading to get detailed information on how to fix an overflowing gas tank.

Refilling fuel view from inside of gas tank of a car - Gas Tank Overflowing When Not Full—What To Do

What To Do When Your Gas Tank Overflows 

Refueling the 1000 liter gas tank of big truck.

If your gas tank starts overflowing when it isn't filled, the first thing you need to do is to check the inner tube of the fuel filler neck. Using a siphon hose to get fuel out of the tank may knock off the hose, so try checking the tube. If the hose isn't in place, you should contact a mechanic for help.

This problem could make the tank not get filled up as it should. Also, the inner hose can get stuck in the fuel sender, leading to inaccurate readings. 

What Do You Do If You Overfill Your Gas Tank?

If you notice that you have overfilled your gas tank, try running your engine while your vehicle isn't moving, and then remove the fuel cap. Also, do not fill the gas tank to the edge of the container. Make sure the fuel nozzle cut-off is in use so you will know when to stop.

If you have gas on the tank breather carbon filter canister, it will provide a code and stop the engine's operation. There might be a need to change your canister

If the excess gasoline touches the outside of your vehicle, clean it off thoroughly using a rag. Remember to wash your hands after this to get rid of the gasoline.

What Happens When You Have An Overfilled Tank?

The vapor intake hole may be covered with liquid gas if you have an overfilled tank. The gas may get trapped in the charcoal canister, causing damage to the canister and other parts of the system. If this happens, your vehicle's check engine light may come on. Repairing this damage could cost a lot of money.

The volume of gasoline expands by about 1 percent for every 15 degrees Fahrenheit. And it’s not unusual for the temperature range of a day to differ by 30 degrees. This means that if you put 15 gallons of gas into your tank when the temperature is low, it will increase by over a quart when it warms up by 30 degrees.
If you have an overflowing tank, gas may be forced into the feed line of the charcoal canister or cause a leak.

How Do You Know Your Gas Tank Is Overfilled?

A person filling up the car in a gas

You should be careful when filling your gas tank so you don't overfill it. An overflowing gas tank can lead to serious problems. When you have an overfilled tank, the gas is likely to overflow onto the vehicle and may touch anything close by.

The act of filling your car’s tank with excess gas is known as gas topping. Fortunately, you can easily avoid overfilling the gas tank of your car. The work of the gas pumps is to halt pumping gas when there is enough gas in your tank.

When the nozzle notices that gas is blocking air in the Venturi tube, it shuts it immediately. The Venturi tube is designed to measure the amount of liquid moving through the pump.

One way to avoid overfilling your gas is by removing the gas pump nozzle from your gas tank and placing it back on the pump when a ‘thunk’ sound is heard. The gas pump nozzle usually makes this sound when your gas tank is full. When the nozzle is removed, the transaction will be stopped. If you overfill your tank, it may start to overflow. 

Can Overfilling Make A Car Stall?

When you have an overfilled gas tank or some gas is heading into the EVAP line, your vehicle may start having problems. An inadequate refuel and fuel cutoff valve may stop the flow of fuel. The refuel valve makes the gas pump stop, prompting the vehicle to stall.

If you are driving your car and it stalls, it could be because of overfilling the gas tank. If this happens, the best thing to do is to stop the car immediately and wait for a few minutes before trying again. Filling up your tank is good, but it shouldn't be done in excess, and waiting till it gets empty is not advisable.

If you keep waiting till your tank is empty, your fuel pump becomes strained. It then begins to suck up dirt and water under your tank, leading to a clogged filter and a need to change the fuel pump assembly.

What Stops Fuel From Overflowing?

An anti-splash valve is found in the fuel fill inlet hose. This valve is responsible for stopping fuel from flowing up the hose when the tank is filled. The anti-splash valve is designed to stop any water from coming in contact with the engine and other components.

A woman pumping gas with a handheld fuel nozzle at a gas station

Can Overfilling Cause A Leak?

Topping off your gas tank puts so much pressure on your evaporative system. It can also lead to a hazardous leak. Gas needs enough space to expand in the tank, and filling up all the space isn't a good idea.

Pressure tends to build in the tank, flooding the carbon filter vapor collection system that is supposed to accommodate only vapor. The overflow affects the way your car works and could damage the engine. 

Why Is My Car Not Starting After Getting Gas?

After filling your tank, you may start finding it too difficult to start your car. This is because an EVAP purge control valve may have stuck open. Anytime you fill your tank with gas, the overpressure of air becomes in need of a place to move to. It then becomes tight with the fuel nozzle.

However, if the valve is open, it will be forced directly into the intake manifold. This makes excess fuel flow into the combustion chamber while turning on the vehicle's engine after buying gas, making startup difficult.

If your car refuses to start after refilling, you can also check your battery connection. If connections aren't in place, make sure to fix them. If your battery is dead, try pushing it from the pump and then jumpstart it.

What is EVAP?

EVAP stands for Evaporative Emission System. It is a system in a vehicle that controls the release of vapors from liquid fuels. The device is designed to prevent the vapor from entering the atmosphere, avoiding pollution.

Apart from helping the environment, it also aids fuel efficiency. Additionally, the system makes your cabin free from gasoline smell. It is usually found on vehicles like trucks, buses, and trains.

Why Does Gas Come Back Out When Filling Up?

Refilling fuel view from inside of gas tank of a car

The reason could be that the fuel vent hose on the fuel filler neck is blocked, preventing the fuel to vent as you add fuel to your tank. You should try getting the hose out and fish it through the vent tube and gas tank with a cleaner or metal.

With time, fuel vapor with debris may block the vent tube, making it not to vent the gas tank. This makes fueling up difficult under heavy load.

To Wrap Things Up

When your gas tank starts overflowing when there is still space in your tank, always check if the fuel filler neck’s inner tube is off. When your gas tank gets overfilled, it can move to the canister and cause damage to the Evaporative Emission System.

Overfilling can lead to a number of problems, including engine troubles and damage to the environment. Fuel can overflow and spill onto the ground, which is an environmental hazard and a safety risk if someone slips on it.

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