Five essential checks before driving during the heatwave

With highs of 37C forecast, it’s not just you who needs to keep cool; the mechanical components under your bonnet can face real problems as temperatures rise.

Last year the RAC reported a 20% increase in vehicle breakdowns when temperatures regularly exceeded 30C, with overheating engines, failing batteries, and tyre blowouts among the most common causes.

With temperatures set to climb further, expert at leading motor retailer Vertu have identified the five areas of your car most vulnerable to heat damage and what you can do to protect them:

1. Check your coolant level before it becomes an emergency

Engine overheating is one of the leading causes of summer breakdowns, and it can escalate quickly. In stop-start traffic or on long motorway stretches, a cooling system running low on fluid can allow engine temperatures to spike. A blown head gasket caused by overheating can cost over £1,000 to repair, with severe cases requiring engine work running into the thousands.

Check your coolant level at least once a fortnight during summer, but only when the engine is completely cold. The reservoir has minimum and maximum markers on the side. If the level sits at or below the minimum, top up with a 50/50 mix of antifreeze and water. If you find yourself topping up repeatedly, book a professional inspection, as this suggests a leak in the system.

2. Test your battery before the heat does the damage for you

Most drivers associate battery failure with frosty mornings, but summer heat causes permanent, irreversible damage that cold weather simply cannot. High temperatures accelerate the chemical reactions inside the battery, causing the electrolyte fluid to evaporate and internal corrosion to build up. The life of a lead-acid battery can be halved for every 8°C rise above 25°C, and the average battery in the UK fails at just 3.2 years.

If your battery is more than three years old, have it tested professionally before the warmest months arrive. Look for visible warning signs: a swollen or bloated casing, white or green corrosion around the terminals, or a noticeably slow engine crank when starting. If you regularly make short journeys under 20 minutes, take a longer drive of at least 30 minutes once a week to allow the alternator to fully recharge the battery.

3. Inspect your tyres when they’re cold, not after a drive

For every 10°C rise in temperature, tyre pressure increases by 1 to 2 PSI. On a hot day, road surfaces can exceed 50°C, placing additional stress on rubber that is already expanding. If a tyre has existing damage, such as a sidewall crack or a bulge, the combination of heat and increased pressure can cause a blowout. According to the Department for Transport, there were 190 tyre-related killed or seriously injured casualties on UK roads in 2023, a 29% increase on the previous year.

Always check tyre pressure when the tyres are cold, before driving or after the car has been stationary for at least two hours. The correct pressure for your vehicle is printed on a sticker inside the driver’s door frame or in the owner’s manual. While checking pressure, run your hand along the sidewalls and inspect for cracks, bulges, or embedded objects. If your tyres are more than five years old, have them professionally inspected regardless of remaining tread depth.

4. Check your brake fluid before a long summer journey

Brake fluid is hygroscopic, which means it absorbs moisture from the atmosphere over time. Even 2% water contamination can lower the fluid’s boiling point by approximately 37°C. During sustained braking in hot weather, particularly on motorway slip roads or downhill stretches, the fluid can overheat. If it boils, steam bubbles form in the brake lines, causing a spongy pedal and a serious reduction in stopping power.

Check your brake fluid level using the reservoir under the bonnet, looking for the minimum and maximum markers. If the fluid appears dark or discoloured rather than clear or light amber, it likely needs replacing. Manufacturers typically recommend changing brake fluid every two years. If you notice a soft pedal, longer stopping distances, or a burning smell after heavy braking, book a brake inspection without delay.

5. Run your air conditioning before you need it most

Air conditioning systems lose refrigerant gradually, typically around 10 to 15% per year. After two or more years without a regas, the system struggles to cool the cabin, forcing the compressor to work harder and increasing fuel consumption. Industry data from 2025 shows a 25% rise in air conditioning warranty claims compared to the same period in 2024, with the average repair cost climbing by 55%.

Switch on your air conditioning for at least 10 minutes once a week, even during cooler months, to keep the system’s seals lubricated and prevent refrigerant leaks. If the air from the vents feels warm or takes a long time to cool down, book a regas. Most manufacturers recommend this every two years, and a standard service typically costs between £50 and £100, far less than a compressor replacement.