What happens when you overfill your gas tank?

Last updated May 11, 2023

Much like adding the wrong type of fuel, overfilling the gas tank can significantly damage your vehicle.

When you overfill your gas tank, this can cause liquid gas to enter the charcoal cannister or carbon filter, which is designed for vapour only. Gas in this system can affect your car’s performance by damaging the engine - and causing it to run poorly.

Therefore, you should take care not to fill your gas tank beyond its capacity. Read our guide to learn the signs that you have overfilled your gas tank, the potential repercussions – and what you can do to remedy an overfilled tank.

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Can I overfill my gas tank?

Yes, it is possible to overfill your gas tank. Filling it past the pump’s first automatic shut-off will overfill the tank and may also damage your car. Overfilling can also affect the environment and even pose a risk to your safety. Besides, fuel can go off, so it doesn’t make sense to fill up to a potentially dangerous level no matter what.

How do you know when you’ve put too much fuel in your car?

If you have put too much fuel in your car, it will overflow and spill out. If the gas tank is filled beyond capacity, the ‘check engine’ light on the dashboard may also illuminate.

Most fuel pumps have an automatic shut-off mechanism, which activates when the fuel tank has reached capacity. If you choose to ignore this, you will overfill your car, which won’t help you to save fuel.

If you overfill your gas tank will it leak?

If you’ve put too much fuel in your gas tank, this can cause a hazardous leak due to the excess pressure in the system.

Will putting too much fuel in my car cause damage?

As we’ve already mentioned, overfilling your fuel tank can cause liquid gas to enter the charcoal cannister or carbon filter.

These systems are designed to work with vapours and not liquids. If you overfill your tank, this can cover the vapour intake hole with gas, which is then sucked into the charcoal cannister. This can damage the cannister and possibly other parts of the system, which can cause the car’s ‘check engine’ light to come on - and could also leave you with a costly repair bill.

Is it safe to overfill my tank?

No, it isn’t safe to overfill your fuel tank. Petrol, in particular, can expand in volume when it is warm - and when the temperature rises during the day, this can be enough to push the fuel into the charcoal cannister’s feed line or force a leak, which is a major safety issue.

Is it a waste of money to overfill my tank?

Filling up your car can be expensive at the best of times (just check our fuel calculator), but overfilling is always a waste of money, particularly if you fill up with premium fuel.

Aside from paying more to fill up and wasting any fuel that spills out of the tank, you will also run the risk of damaging your vehicle – and incurring eye-watering repair costs!

If saving money on fuel is your goal, consider choosing an automatic car as opposed to a manual vehicle - and seeking out the cheapest petrol and diesel prices near you with the various tools and apps available online. By following these steps, you can reduce your fuel spend, without the risk of damaging your vehicle.

What should I do if I’ve overfilled my car with gas?

You should clean up any spillages and wash any fuel off your car, if it has leaked out.

If the fuel is in the filler tank, don’t start the engine; wait for a few minutes until the fuel has filtered down. If the fuel doesn’t filter down, it won’t be safe to drive - and you’ll need to have your car towed.

However, if you are able to start your car, make sure to drive it at a high RPM to burn any excess fuel in the tank, so that it is no longer filled beyond capacity.

Frequently Asked Questions

Yes, overfilling your gas tank can cause the car to stall. The crankshaft might be dipping down into the oil (which it isn’t supposed to touch). This will cause it to slow down, preventing it from revving up to a normal speed.

Yes, overfilling the gas tank can trigger the ‘check engine’ light on your car’s dashboard.

In extreme cases, overfilling a gas tank could cause a fire or an explosion, due to the spillage of fuel - and fuel reaching components that it shouldn’t.