Overheating
Check coolant level and condition. Look for leaks under the car after it has been parked. If the temperature gauge climbs in traffic, turn the heater on full to pull heat from the engine, and pull over safely if it keeps rising. Never open a hot radiator cap.
Tyres
Heat raises tyre pressure and underinflated tyres flex more and get hotter still, which is how motorway blowouts happen. Check pressures cold, set them for a loaded car, and inspect for cracking on older tyres. Tyres over seven years old are a risk regardless of tread.
Air conditioning
If the air-con is weak, have it regassed before the trip rather than during a heatwave queue. Running it also helps demist in sudden summer downpours.
The car as a hot box
Never leave children or dogs in a parked car in summer, even briefly. Carry water for everyone. Sunshades and ventilation make a big difference to how a car cools on return.
Hay fever and driving
Some antihistamines cause drowsiness and it is an offence to drive while impaired by medication. Choose a non-drowsy option, keep windows closed and use the pollen filter setting.
Holiday traffic
Stop-start motorway traffic in heat is hard on cooling systems and clutches. Leave early, take breaks every two hours, and keep the fuel or charge above a quarter so you are not caught out by a long diversion.
Cover for the holiday
A summer trip is the classic case for onward travel: a hire car means the holiday continues while the car is repaired. If you are crossing the Channel, European cover is not optional.