Drivers are being warned not to press the air conditioning button as it can increase fuel usage by up to 20%.
As the price of fuel continues to increase and with scorching hot weather forecasted this week, motorists will be looking to keep cool in the heat.
And with drivers paying on average 178.93p per litre for petrol and diesel owners paying 189.30p - burning through fuel can be extremely costly.
While the RAC says prices should fall, Express.co.uk reported, many motorists will still be looking at ways they can save and make their fuel last longer.
When driving in warm weather, motorists will usually opt for having the windows open or by using air conditioning.
However, many motorists often overlook their impact on their fuel efficiency - with both options having a huge impact on how fuel is used.
Air conditioning is very energy intensive, while open windows can reduce the drag of the car, making the car work harder and burn through the fuel quicker.
While both can be used, there are points at which one or the other is more beneficial to the driver and the car.
Chris Evans, head of content at Leasing.com, highlighted the benefits of using both air conditioning and having the windows open.
He referenced a 2004 study by the Society of Automotive Engineers (SAE), which looked at the impact of windows open against air conditioning in larger saloons and SUVs.
In the study, there were plenty of variables including how much the windows were open, the aerodynamics of the different cars and how long someone might use the air conditioning.
He said: "As such, the 45mph figure is a guide, but a fairly good one.
“While all this might seem like a minor issue, getting it wrong can have a notable impact on your fuel economy.
“Using AC can increase your fuel consumption by as much as 10 percent but opening the windows at higher speeds can increase fuel consumption by as much as 20 percent.”
A number of other studies have also followed, one of which found that hybrid car fuel economy is harder hit by air con use than conventional combustion-only cars.
More research, from Emissions Analytics, found that the impact of air conditioning on hybrid fuel economy was almost twice as much.
Fuel efficiency dropped 6.1 percent in a hybrid car on average, compared to just 3.8 percent for standard petrol car and 4.6 percent for a diesel.
Mr Evans continued saying: “While the 45mph line is a good guide, things get a bit more complicated when you are in bumper-to-bumper traffic.
“In these situations, it is probably best to avoid using air con or opening your windows.
“However we know that in hot conditions that might be uncomfortable, so as a solution you could turn on the air con but close your air vents.
“The air con merely recycles the cabin air rather than drawing the air from outside, where there is nose-to-tail line of traffic all belching out exhaust fumes.”
Other options for keeping the car cooler and not relying on air conditioning include parking in the shade or in a garage.
Tinted windows could also provide benefits for drivers, as will heat deflectors.
A car window tint can effectively reduce the heat given off by direct sunlight by as much as 70 percent inside a car.
Since the car will be cooler, drivers may be less likely to use the AC.
