Hot Weather Car Myths Busted: Expert Tips for Summer Driving

As England swelters under another Amber Heat Health Alert, and the fourth heat wave of the summer, soaring temperatures aren't just uncomfortable for drivers - they can quietly wreak havoc on cars. From tyres and batteries to fuel systems and cooling components, prolonged 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

Some drivers believe that summer heat causes petrol 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 is lost as a result of the heat, but the amount is usually negligible unless the system or cap fails - around just 1–2% per summer at most. In the grand scheme of things, you're unlikely to notice.

The only scenarios where fuel might escape are rare and avoidable. Overfilling the tank on a very 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. A cracked or hardened fuel cap seal, a warped cap, or one that hasn't been tightened correctly - each of these faults can also trigger a check engine light, reduce fuel economy, and leave stains around the filler opening.

To prevent problems, avoid topping up beyond the first click at the pump, especially in hot weather, and check that your fuel cap clicks firmly into place. If you notice a persistent fuel smell or visible wear on the cap's seal, replace it; It's an 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

Far from being harmless, letting your car run while the temperature gauge climbs toward (or worse, into) the red zone is a serious risk.

This isn't a warning to ignore, as it's telling you that the engine is at risk of overheating. The consequences can range from a warped cylinder head and blown head gasket to a cracked engine block, ruptured hoses, or even an under‑bonnet fire.

If your engine temperature gauge starts to creep towards the red zone, it's advisable to pull over safely at the first sign of trouble - whether that's the gauge peaking, steam rising from the bonnet, a dashboard warning light, or even a pungent, sweet odour of coolant.

If you're not able to pull over safely, turning off air conditioning and blasting the heater on full can help redirect heat away from the engine and lower its temperature, but this should only ever be seen as a temporary solution until you can stop safely to manage the problem properly.

Once you've pulled over and turned off the engine, let it cool undisturbed for at least 30 minutes before checking coolant levels. It's important to note that you should never open the radiator cap while it's hot, as it can spray boiling coolant and steam.

Even if your car seems to have recovered, you shouldn't drive off assuming all is well. Underlying causes like coolant leaks, a failing water pump, a blocked radiator, or a broken thermostat often require immediate professional diagnosis to prevent recurrence or worse damage.

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

With all the advancements in motoring tech, you'd be forgiven for assuming that today's vehicles are immune to the problems hot weather can bring. In reality, prolonged heat still exposes weaknesses - and during a heatwave, those weaknesses can lead to breakdowns.

Breakdown providers report seeing around 20% more callouts during periods of extreme heat, with coolant-related issues almost doubling during one recent hot spell. Newer vehicles aren't spared from these issues, as heat accelerates the wear and tear on key systems.

Tyres are among the most vulnerable components. In high temperatures, air inside tyres expands, increasing pressure and the likelihood of blowouts, especially if tyres are already worn or underinflated.

Batteries also suffer, as under-bonnet temperatures can climb to 40–50°C even on a relatively mild day, speeding up corrosion and causing battery fluid to evaporate. Just an 8 °C rise above optimal operating temperature can halve a battery's lifespan, meaning a particularly hot spell can turn a healthy battery into a sudden failure risk.

Prolonged periods of hot weather also increase the likelihood of coolant leaks, failing thermostats, and radiators struggling to dissipate heat efficiently, all of which can lead to overheating and expensive engine damage if ignored.

The truth is that no matter how advanced your car is, extreme heat will highlight any underlying weaknesses. The best defence is regular maintenance: check coolant levels and hoses, test battery health, and inspect tyre pressure when the tyres are cold. These small checks can make the difference between a smooth summer drive and an unwelcome stop at the roadside.

Myth 5: Opening windows cools the car faster than using the air-con

There's some truth to this idea, but it's far from the full picture.

When temperatures soar, the air inside a parked car can reach over 50°C. When you first get into your car, rolling down the windows (or better yet, opening doors on opposite sides to create a cross-breeze) is an effective way to flush out the hottest air, especially if you're only moving slowly through town or pulling away from a parking space.

At higher speeds, however, it's a different story. Open windows actually disrupt the car's aerodynamics and create drag, forcing the engine to work harder. Tests have shown that this extra resistance can increase fuel consumption by as much as 20% at speeds above 40mph. In reality, open windows at high speeds can end up costing more in fuel than running the air conditioning.

Sadly, even air con isn't free to run; powering the compressor typically increases fuel use by around 8–10% - but once you're at motorway speeds, it's generally the more efficient option.

Overall, it's best to start your journey with the windows open for a minute or so to flush out any trapped heat, then close them and switch the air-con to recirculation mode so it's cooling air that's already been chilled. Keep the system well maintained with fresh filters and topped-up refrigerant, and it will not only cool the cabin faster but also use less fuel in the process.

Myth 6: Hot weather damages your car battery

Sadly, this particular myth is true. Research shows that high temperatures accelerate the chemical reactions inside a battery, speeding up internal corrosion and causing the liquid electrolyte to evaporate. The hotter it gets, the faster the damage: for every 8°C rise above the ideal operating temperature (around 25 °C), a battery's lifespan can be cut by as much as half.

Conditions under the bonnet can be far hotter than those outside. On a mild 22°C day, engine bay temperatures can climb to 40-50°C. As you might imagine, they can exceed that during a heatwave. Exceptional heat breaks down the battery's internal plates and dries out fluid more quickly, leaving the battery with less capacity to hold charge. Over time, this leads to sluggish starting, dimming headlights, erratic electrical performance, or in severe cases, visible swelling of the battery casing.

It's easy to forget to perform routine checks on your car, but they're particularly important during hot spells. Generally speaking, if your battery is more than three years old, extreme heat makes it far more likely to fail without warning. Simple maintenance like cleaning corrosion from the terminals, ensuring the battery is securely mounted, and checking electrolyte levels in serviceable batteries can help prolong its life. Some modern AGM or EFB batteries are better at coping with heat, but even still, they're not immune.

Myth 7: Tyres are at less risk in hot weather than in cold

It's a dangerous misconception to think tyres only face real danger in icy, winter conditions. In fact, high summer temperatures can be just as punishing - sometimes even more so.

Heat makes the air inside tyres expand, which can increase pressure beyond the manufacturer's recommended range. If a tyre is already overinflated, worn, or damaged, that extra pressure raises the likelihood of a sudden blowout, particularly at motorway speeds where the tyre is under sustained load.

Heat also speeds up the deterioration of existing tyre weaknesses. A small bulge, cut, or crack that might have been stable in cooler weather can worsen rapidly in a heatwave, sometimes with little or no warning before failure.

Road surfaces themselves also add further risk. During heatwaves, tarmac temperatures can soar well above the air temperature - often exceeding 50 °C - which softens the rubber of tyres and increases the potential for wear. Long drives on hot motorways also cause heat to build up inside the tyre structure, further weakening it over time.

Until we invent flying cars, there's not much you can do to avoid the impact of road surfaces on your tyres. The safest way to minimise the risk is to check tyre pressures regularly, doing so before driving and early in the day, when the tyres are cold. This ensures an accurate reading and prevents overinflating based on a hot tyre's already expanded pressure. Drivers should also inspect tread depth, check for uneven wear, and look closely for cracks or bulges in the sidewall.

Ultimately, while winter driving requires caution for grip and traction, summer heat demands equal vigilance for pressure and structural integrity. In both cases, the best defence is regular maintenance and knowing the condition of your tyres before you set off.