Overfilling your fuel tank is a fast way to cost you dearly

It’s a habit many have developed over the years but experts warn that pumping fuel into your car after the first click could end in a costly repair bill.

In the days when most motorists paid for fuel by cash, it was common practice to pump fuel into the car until you had a round number on the bowser readout.

These days most of us are using our phones or credit cards to tap and go, so there’s no need to keep pumping. But there’s another reason why it’s time to break this habit.

Modern cars switch off the fuel flow with a click at a certain level to protect the car’s vapour recovery unit, a complicated piece of equipment designed to stop potentially harmful fumes escaping from the petrol tank during refuelling.

The units have a carbon canister to soak up fumes from the petrol tank. The fumes are then fed back through the fuel lines into the combustion chamber and burned off.

Motoring expert Mark Short, from Motorsport Safety and Rescue, says people who continue to pump fuel after the first click run the risk of flooding the vapour recovery system.

“The charcoal canister and purge valves are meant to eat up the smell and fumes of the petrol. They’re the breathing system of your fuel tank. If you keep filling it up you’re effectively flooding the breathing system,” he says.

“There’s no good reason to do it. You can damage the ventilation and emissions system and things like charcoal canisters and purge lines can be quite expensive to replace,” he says.

Car makers are unlikely to cover any damage under warranty either, as most owner’s manuals specifically warn against over filling.

The Haval Jolion’s user manual says: “Fill to the first automatic stop of the filling gun. Otherwise the fuel can easily enter into the carbon canister and then shorten its service life.”

The manual points out that overfilling can also lead to spillage, which “may corrode the painted surfaces” .

Plus you will be paying for fuel you’ll never use. And there’s another unpleasant side effect of overfilling.

“If the charcoal canister does get fuel in it you can make the car smell of petrol for days,” Short says.