Hot Weather Car Myths - and How to Protect Your Car in Summer

Heatwaves and soaring temperatures are becoming more common but what effect does hot weather have on our cars and how can you best protect your car?

From tyres and batteries to fuel systems and cooling components, extreme heat exposes weaknesses that might otherwise go unnoticed.

Even so, many of the things drivers believe about hot weather and cars simply aren’t true. The team at personalised number plate supplier Regtransfers got in touch with some research that is too good not to share and offers more insight on this topic.

But first a few quick tips to protect your car in summer.

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. You can find the recommended tyre pressures in the owner’s manual or on a label inside the driver’s door.

• Be clever about parking the car in shade where possible or use a windscreen shade to keep the heat out.

• Replace older car batteries before they fail.

• Get fresh air circulating in a hot parked car with open windows briefly, then switch to A/C recirculation for  more efficient cooling.

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

Reality: Partially true

Modern fuel systems are sealed and designed to prevent petrol either evaporate from the tank or leak out through the fuel cap. 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.

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.

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

Reality: False

Driving a car that is overheating, puts your engine at serious risk. It can cause a warped cylinder head, blown head gasket, cracked engine block, ruptured hoses or even a fire.

If the gauge starts to rise beyond normal operating temperature, pull over as soon as it’s safe. Warning signs include steam from the bonnet, a dashboard temperature warning or sweet smell of coolant. If you 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 until you can pull over safely.

Once stopped, turn off the engine and wait at least 30 minutes before checking coolant levels. Never open the cap when hot because 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.

3. 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. Tyres are especially vulnerable because heat makes the air inside expand, increasing pressure and the risk of a blowout, especially if tyres are worn or already overinflated. Extreme heat can also affect car batteries and cut their lifespan. Cooling systems come under strain, with hot weather increasing the risk of coolant leaks, failing thermostats and radiators struggling to dissipate heat effectively.

The best defence is regular maintenance like checking coolant levels and hoses, testing your battery health and measuring tyre pressures when the tyres are cold.

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

Reality: True…but also false

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 a hot parked car.

When driving at higher speeds however, open windows create aerodynamic drag that force the engine to work harder. Tests show this can increase fuel use by up to 20% at motorway speeds, often making air conditioning the more efficient option. Running the air con 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 way to cool the car is to do both. So open the windows briefly to vent heat, then close them and switch to air con in recirculation mode so it’s cooling already chilled air. Keep the system maintained for more efficient cooling.

5. Myth: Hot weather damages your car battery

Reality: True

High temperatures are tough on batteries because it accelerates chemical reactions inside the battery that speed up corrosion and causing the electrolyte fluid to evaporate. The hotter it gets, the faster this damage occurs.

Conditions in the engine bay are far hotter than the air outside. As the temperature climbs, 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.

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

Reality: False

Tyres are not just 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 without warning.

The best approach is to check tyre 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.

Extra Summer Driving Tips

• Plan your trips: Travel early or late to avoid the hottest hours and heavy traffic.

• Pack smart: Carry drinking water, sun protection, snacks, a phone charger and a roadside kit.

• Protect the interior: Use sunshades, open windows slightly when parked, and avoid leaving electronics, aerosols, or medicines in the car.

• Look after yourself: Fatigue and dehydration rise in hot weather. Take regular breaks, bring lots of water with you and don’t underestimate how the heat can affect your concentration.

• Check wipers and washer fluid: Insects and dust build up quickly in summer, so clear visibility is essential.

Heat is just as challenging for your car as winter cold. A few minutes of preventive maintenance around tyres, fluids and battery checks can make the difference between a smooth summer road trip and being stranded by the roadside.