Drivers told to press 1 switch on Friday to avoid 'draining fuel'

Motorists have been urged to press one common car button found in every vehicle on the roads as hot weather hits the UK this week. Road users sitting in sweltering cabins may automatically lean down and switch on their air conditioning to stay cool.

However, switching on the device even in hot weather could backfire with petrol and diesel owners likely to use up more fuel. Instead, Tim Rodie, Motorpoint’s resident driving expert, stressed opening windows “at lower speeds” could be better than turning on air conditioning. Those travelling at lower speeds will definitely save money but Tim warns this could change as road users build up speed.

Tim explained: “While you might be planning on setting your air conditioning to full blast when driving in spells of hot weather, it can really be a drain on your fuel.

“Motorists looking to go longer between filling up might think just opening the windows is an obvious alternative, but at higher speeds, this can make your car less aerodynamic – meaning you’ll be using more fuel.

“As a rule, opening your windows is best when driving around at lower speeds around town and air conditioning is more efficient if you’re on the motorway. So, keep this in mind and be sure to mix it up on long car rides.”

On average, switching on air conditioning units can increase fuel consumption by between 8% to 10%.

According to Kwikfit, this would translate to using 0.2 to 0.4 litres of fuel per hour.

The UK is set to bask in sweltering conditions over the coming week with the Met Office predicting temperatures as high as 27 Celsius on Friday.

The warm weather will continue into the weekend with meteorologists predicting conditions of up to 23 Celsius on Saturday and Sunday.

The RAC said: “Generally speaking, keeping your windows up and using the air-con at speeds above 45mph is the most efficient way to keep your cabin cool.

"Below that speed, think about rolling your windows down.

“That’s the conclusion of a 2004 study by General Motors and engineering standards organisation SAE, which compared fuel use in a saloon and SUV at speeds of 31mph, 50mph and 68mph.”