Motorists are being told to stop filling their petrol tank after the first 'click' at the pump.
An industry expert says the practice known as 'topping off' could not only see them waste money as they fill up, but could also inflict on their vehicle as much as £500 of damage.
Graham Conway, managing director of UK leasing firm Select Car Leasing, says drivers should fight the urge to round up to the nearest pound, reports MEN.
Explaining how going beyond the very first click is likely to cost you, he said: “That’s because it’s likely to still dispense some fuel that won’t end up in your tank.
"If you ignore the first click you could be filling past the top of the fuel tank port, and that extra fuel will end up running into the small drain under the entry and onto the ground beneath your vehicle. On some pumps the extra fuel may be sucked back into the pipe.
"This means you are paying the petrol station to give them back their own fuel.
But Graham said a more serious issue lies in the potential damage that can be caused to the vapour recovery system, which stops evaporated petrol or diesel escaping when the petrol cap is released by capturing it in a charcoal canister.
Forcing surplus petrol or diesel into the tank can "propel liquid fuel into the pipes" , which damages the vapour recovery system.
“That means you will soon see warning lights on your dashboard and run the risk of failing emissions tests. You’ll also be looking at an expensive repair bill, possibly up to £500. That’s something definitely worth avoiding during the current cost of living crisis.”, he said.
The Select Car Leasing chief finished by recommending people stave off the "obsessive-compulsive side to their character" when filling up, and look instead to get the best value for money.
Fuel prices have been falling back to levels seen at the start of the year in recent weeks, according to data from the RAC, after reaching a record high of 191.43p per litre in July.
