Drivers are being urged to fill up their vehicles before Monday, as a return to hot weather across parts of the UK could cause fuel to run down more quickly than usual, potentially catching unsuspecting motorists off guard. The Met Office has forecast a heatwave starting Sunday, with temperatures peaking on Monday in London and southern England, reaching 30°C on Sunday and rising to 32°C on Monday, with similar temperatures expected for most of the following week.
How Hot Weather Affects Fuel Consumption
During hot weather, petrol and diesel can run down more quickly due to driver behaviour and the effects of high temperatures on fuel economy. According to the US Department of Energy, while hot weather can initially improve fuel economy as engines warm up faster and summer-grade gasoline has slightly more energy, the use of air conditioning (A/C) to stay comfortable significantly reduces fuel efficiency. The department states: "Under very hot conditions, A/C use can reduce a conventional vehicle's fuel economy by more than 25%, particularly on short trips. The A/C's effect on hybrids, plug-in hybrids, and electric vehicles (EVs) can be even larger on a percentage basis."
Drivers also tend to open windows, which increases aerodynamic drag and further decreases fuel economy. These factors can make fuel gauges inaccurate, giving a false sense of how much fuel remains.
Fuel Prices Remain High
Fuel prices have surged in recent months due to the conflict in Iran, and despite a slight cooling, remain significantly higher than before. According to the RAC, the average price of petrol is currently 154.72p per litre, while diesel stands at 174.30p per litre. With such high costs, wasting fuel through inefficient driving practices can be costly.
Experts Warn Against Running on Empty
Experts at PassMeFast.co.uk advise drivers to refuel earlier than usual in hot weather. They explain: "When it comes to topping up the petrol in your car, there are two kinds of people: those who refill as soon as the fuel tank gets to around a quarter full, and those who are happy to drive around with the fuel warning light on. The thing is, when the weather's nice and warm, your car's fuel levels drop a lot quicker than usual. This means you can't rely on your normal estimations of how much time you have left before needing to fill up. To avoid getting stuck in the middle of nowhere, or at the centre of a traffic jam on a hot day (both nightmare scenarios), make sure you head to the petrol station in good time. Playing it close to the line is just not worth it if the sun's out!"
The Myth of Exploding Fuel Tanks
Some drivers have been warned not to fill up during hot conditions due to a risk of the vehicle exploding in the sun. However, this is a myth. RAC spokesperson Rod Dennis said: "There is no truth in this. All fuel systems on passenger vehicles are designed to cope with any expansion of fuel, or vapour coming from the fuel. There is no risk of explosion from filling up a fuel tank fully and drivers should have no concerns in doing so."
Optimal Temperature for Fuel Economy
Experts note that the optimal temperature for fuel economy is between 15°C and 20°C. Fuel Finder UK explains: "According to official fuel economy tests, your car's efficiency drops by around 10% at -5°C compared to 20°C. For short trips under four miles, that penalty can reach 20% or more." However, once temperatures hit 32°C, engine efficiency is reduced and there is a risk of overheating. Therefore, while 20°C offers better fuel economy than very cold temperatures, the gains are lost as the mercury rises further.
