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As many parts of the world experience prolonged heatwaves, soaring temperatures aren’t just uncomfortable for drivers – they can wreak havoc on cars. From tyres and batteries to fuel systems and cooling components, extreme heat exposes weaknesses that might otherwise go unnoticed. Even so, many of the “facts” drivers believe about hot weather and cars simply aren’t true. With insights from trusted sources, fresh UK data and the car enthusiasts at personalised number plate supplier Regtransfers, here’s the truth behind some of the most persistent myths.

Myth: Hot weather makes petrol “evaporate” from the tank

Reality: PARTIALLY TRUE

Some drivers believe that summer heat causes petrol (gasoline) to either evaporate from the tank or leak out through the fuel cap. In reality, modern fuel systems are sealed and designed to prevent both. Cars built in recent decades use an EVAP (Evaporative Emission Control) system, which traps fuel vapour and routes it back into the engine to be burned. It’s true that a small percentage of fuel can be lost as vapour during very hot weather, but the amount is usually negligible unless the system or cap fails – typically no more than 1-2% per summer.

Fuel escape is rare and preventable. Overfilling the tank on an extremely hot day can cause fuel to expand and push small amounts through the overflow system, but not past a properly fitted, airtight cap. When petrol genuinely “goes missing,” it’s almost always due to a fault, such as a cracked or hardened fuel cap seal, a warped cap, or one that hasn’t been tightened properly. These issues can also trigger a check engine light, reduce fuel economy, and leave stains around the filler opening.

To avoid problems, don’t top up beyond the first click at the pump in hot weather, and make sure your fuel cap clicks firmly into place. If you notice a fuel smell or visible wear on the cap’s seal, replace it – it’s a quick, inexpensive fix that protects both your fuel and the environment.

Myth: It’s fine to drive if the engine temperature gauge creeps into the red

Reality: FALSE

Far from harmless, driving while your temperature gauge climbs toward – or into – the red zone puts your engine at serious risk. Overheating can cause a warped cylinder head, a blown head gasket, a cracked engine block, ruptured hoses, or even an under-hood fire.

If the gauge starts to rise dangerously, pull over as soon as it’s safe. Warning signs include steam from the hood, a dashboard temperature warning, or the sweet smell of coolant. If you absolutely can’t stop immediately, switching off the air conditioning and turning the heater on full can help draw heat away from the engine – but this is only a temporary measure to buy you time to pull over safely.

Once stopped, turn off the engine and wait at least 30 minutes before checking coolant levels. Never open the radiator cap when hot – pressurised coolant can spray out, causing burns. Even if the temperature drops, don’t assume the problem has fixed itself. Overheating is often caused by coolant leaks, a faulty water pump, a blocked radiator, or a broken thermostat – all of which require professional attention.

Myth: Modern cars are built tough enough to shrug off heat-related problems

Reality: FALSE

Today’s vehicles are engineered to handle a wide range of conditions, but prolonged heat still exposes weak points – and breakdown services around the world see spikes in calls during hot spells.

Tyres are especially vulnerable. Heat makes the air inside expand, raising pressure and increasing the risk of a blowout, especially if tyres are worn or already overinflated. Batteries also suffer – under-hood temperatures can easily reach 104-122 °F (40-50 °C), even on mild days. Just an increase of 15 °F (8 °C) above the ideal operating temperature can cut a battery’s lifespan by half. Cooling systems also come under strain, with hot weather increasing the risk of coolant leaks, failing thermostats, and radiators struggling to dissipate heat effectively.

The best defence? Regular maintenance. Check coolant levels and hoses, test your battery health, and measure tyre pressure when the tyres are cold. Small preventative steps can mean the difference between a smooth summer drive and being stranded on the roadside.

Myth: Opening windows cools the car faster than using the air-con

Reality: TRUE… BUT ALSO FALSE

When you first get into a parked car, the cabin temperature can easily exceed 122 °F (50 °C). In that situation, opening the windows – or even better, opening opposite doors briefly to create a cross-breeze – is an effective way to let trapped hot air escape, particularly if you’re moving slowly through city streets or just starting out.

At higher speeds, however, open windows create aerodynamic drag that forces the engine to work harder. Tests show this can increase fuel use by up to 20% at highway speeds, often making air conditioning the more efficient option. Running the A/C does use extra fuel – typically around 8-10% more – but at speed, the drag from open windows costs more in efficiency than cooling the car with air-con.

The most efficient method combines both: open the windows briefly to vent heat, then close them and switch to A/C in recirculation mode so it’s cooling already-chilled air. Keep the system maintained with clean filters and topped-up refrigerant for faster, more efficient cooling.

Myth: Hot weather damages your car battery

Reality: TRUE

High temperatures are tough on batteries – in fact, heat often causes more damage than cold. It accelerates chemical reactions inside the battery, speeding up corrosion and causing the electrolyte fluid to evaporate. The hotter it gets, the faster this damage occurs: every 15 °F (8 °C) rise above the ideal operating temperature of around 77 °F (25 °C) can cut a battery’s lifespan by up to half.

Under-hood conditions are far hotter than the air outside. On a mild day, temperatures around the battery can still hit 104-122 °F (40-50 °C), and during extreme heat, they can climb even higher. Over time, this leads to reduced charging capacity, slower engine starts, dimmer lights, and in severe cases, visible swelling of the battery casing.

If your battery is more than three years old, the risk of sudden failure in hot weather increases. Simple checks – like cleaning terminal corrosion, ensuring the battery is securely mounted, and monitoring voltage or charge levels – can help prolong its life. AGM or EFB batteries tend to handle heat better, but they’re not immune.

Myth: Tyres are at less risk in hot weather than in cold

Reality: FALSE

It’s a mistake to think tyres are only a concern in winter. In hot conditions, air inside the tyres expands, raising pressure beyond the manufacturer’s recommendations. If tyres are already worn, damaged, or overinflated, the risk of a blowout rises sharply – especially during long, high-speed drives.

Heat also worsens any existing weaknesses. A small bulge, crack, or cut in the rubber can deteriorate rapidly in hot weather, sometimes with no warning before failure. Road surfaces compound the problem – asphalt can reach over 122 °F (50 °C) in strong sun, softening the rubber and increasing wear. Long drives on these surfaces also raise the tyre’s internal temperature, further weakening it.

The safest approach is to check pressures early in the day, before driving, when tyres are cold. Inspect tread depth, look for uneven wear, and check for cracks or bulges in the sidewalls. Hot-weather driving demands the same vigilance for tyre safety as winter conditions do for grip.

Quick Tips to Protect Your Car in the Heat

·         Check coolant and oil levels before long trips – never open a hot coolant cap.

·         Measure tyre pressure when tyres are cold, inspect for wear or damage, and avoid overinflation.

·         Park in shade, consider heat-resistant battery types, and replace older batteries before they fail.

·         Vent the cabin with open windows briefly, then switch to A/C recirculation for efficient cooling.

·         Use sunshades, and avoid leaving electronics, aerosols, or medications in hot cars.

·         Carry water, sun protection, a phone charger, snacks, and a basic roadside kit.

·         Travel early or late to avoid peak heat and heavy traffic.