Drivers of petrol and diesel vehicles are being urged to fill up before Tuesday if possible, as the return of hot weather this weekend could lead to increased fuel consumption and catch unsuspecting motorists off guard.
Heatwave Forecast
On Tuesday, June 23, temperatures are set to soar to a sweltering 34°C in London, according to the Met Office, while most of England and Wales will see temperatures exceeding 30°C. The Met Office has issued a serious amber weather alert for extreme heat from 1am on Monday until 11.59pm on Tuesday, with temperatures peaking on Tuesday.
Impact on Fuel Economy
Many drivers may not realize that hotter weather poses an unexpected risk to their fuel tank. During hot weather, petrol and diesel can run down more quickly than normal due to driver behavior, and extreme heat can affect fuel economy. Fuel prices have surged in recent months due to the conflict in Iran, and despite a slight recent cooling, they remain significantly higher than before. Currently, petrol averages 154.72p per litre, and diesel is 174.30p, according to the RAC, so drivers will want to avoid wasting any fuel.
Cars use more fuel during hot conditions, both directly and through driver behavior. The fuel gauge may become inaccurate and not properly indicate how much fuel remains. According to the US government, drivers tend to engage in behaviors that consume more fuel in warmer weather, such as opening windows and using air conditioning.
The US Department of Energy states: "Hot weather can increase fuel economy - the engine warms up to an efficient temperature faster; summer grades of gasoline can have slightly more energy; and warm air causes less aerodynamic drag than cold air. However, keeping comfortable in hot weather by rolling down the windows or using the air conditioning (A/C) can reduce fuel economy. Running the vehicle's air conditioning is the main contributor to reduced fuel economy in hot weather. Its effect depends on factors such as outside temperature, humidity, and sun intensity. 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."
Risk of Getting Stranded
Another reason to fill up before warmer weather is to avoid getting stranded in traffic on a hot day. Experts at PassMeFast.co.uk 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!"
Myth of Explosion Risk
Drivers have previously 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
In terms of running a car at its most fuel-efficient, there is a sweet spot between cold and hot weather where performance is optimal. 20°C offers better fuel economy than very cold temperatures, but as the temperature rises, the gains are lost. 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." The sweet spot for fuel economy is between 15°C and 20°C, but once temperatures hit 32°C, engine efficiency is reduced and there is a risk of overheating.
