The UK has seen its share of heatwaves in recent summers, and while sunshine makes for pleasant road trips, soaring temperatures can be tough on cars. From tyres and batteries to fuel systems and cooling components, hot weather exposes weaknesses that might otherwise go unnoticed. Despite this, many drivers still believe persistent myths about cars in the heat. With insights from car enthusiasts at personalised number plate supplier Regtransfers, lets separate the fact from the fiction when it comes to hot weather car myths.
1. Petrol evaporates in hot weather
Partially true
Some drivers worry that petrol vanishes from the tank during the summer. Modern cars, however, are fitted with sealed fuel systems and EVAP controls, which capture vapour and feed it back into the engine. While a tiny amount of fuel may evaporate during extreme heat, it’s usually no more than 1–2% each season.
However, fuel loss is far more likely if the cap isn’t airtight. Cracked seals or loose fittings can cause leaks and poor fuel economy. To avoid issues,, don’t top up past the first click at the pump on a hot day, and replace worn fuel caps promptly.
2. It’s safe to drive if the engine temperature is in the red
False
Letting your car overheat is one of the quickest ways to damage an engine. Risks include warped cylinder heads, blown gaskets, or even under-bonnet fires. If your gauge begins creeping into the red, pull over safely as soon as you can.
Tell-tale signs include steam rising up from the bonnet, a sweet smell of coolant, or dashboard alerts. If you can’t stop straight away, turning off the air-con and running the heater full blast can temporarily draw heat away from the engine – but it’s only a short-term fix. Never open a hot radiator cap immediately after stopping; it’s best to wait at least half an hour before checking coolant levels.
3. Modern cars are immune to heat
False
Even with advanced engineering, high temperatures still strain key systems. Tyres are especially vulnerable, with heat causing internal pressure to rise and increasing the risk of blowouts. Batteries suffer too, as under-bonnet temperatures can easily exceed 40–50 °C, shortening their lifespan.
The best defence is preventative care: check coolant levels, keep an eye on hoses, and measure tyre pressure when the tyres are cold.
4. Opening windows cools the car faster than air-con
True – but not always
At low speeds or when you first get into a sweltering car, opening the windows or doors briefly is the quickest way to release trapped hot air. But at higher speeds, open windows create drag, forcing the engine to work harder and wasting more fuel than running the air-con.
The most efficient method is a mix of both: vent the cabin quickly with open windows, then switch to air-con on recirculation mode to cool the already chilled air.
5. Hot weather damages car batteries
True
Heat can be more harmful to batteries than cold. It speeds up chemical reactions inside, causing corrosion and fluid evaporation. Every 8 °C rise above the ideal operating temperature (around 25 °C) can cut a battery’s lifespan by up to half.
If your battery is over three years old, consider testing or replacing it before summer journeys. Clean terminals, secure mounts, and regular voltage checks all help prolong life.
6. Tyres are only a winter worry
False
While icy conditions are known for reducing grip, hot weather can be just as risky. Rising air pressure, weakened rubber, and scorching tarmac all add to the danger. Tyres with existing cracks, bulges or low tread are more likely to fail on long drives in the heat.
Check pressures before setting off – ideally in the morning, when tyres are cold – and inspect tread and sidewalls for damage.
And for summer journeys, it’s not just your car you need to prepare. Planning pit stops at scenic locations can make long drives more enjoyable – whether you’ll be enjoying a relaxed coastal stay in Wales, or heading a little further afield. Don’t forget to prep a road trip playlist – a good car sing-a-long always helps to wile away the hours!
Can you think of any other common myths about hot cars? Let me know in the comments and I might add it to my list.