How do I get a car ready for hot weather?
The checks that stop a car overheating or breaking down in a heatwave, plus keeping the cabin, the paint and the interior liveable.
- Difficulty
- beginner
- Time
- 40 min
- Read
- 4 min
- Safety
- warning
Short answer
Check the coolant level and have its condition assessed, make sure the air conditioning works before you need it, check tyre pressures against the loaded figures, and keep the interior out of direct sun with a screen. Never leave children or animals in a parked car.
British cars spend most of their lives cool and damp, so the first genuinely hot week finds every weak cooling component at once — usually in stationary traffic, which is when a car is least able to cool itself.
Safety
What you'll need
- A windscreen sunshade
- Interior protectant for plastics and leather (optional)
- A cool box for long trips (optional)
Step by step
- Check the coolant level cold and look at the hoses.Perished, swollen or crazed hoses fail in heat. Squeeze them gently when cold — they should feel firm and springy, not soft or crunchy.
- Have the cooling system checked if the car is older.Radiator, fan and thermostat all matter most in queueing traffic, where there is no airflow. A cooling fan that is not cutting in shows up only when it is hot.
- Test the air conditioning before a heatwave.Run it on maximum cold with recirculation on and feel the vents. Weak or warm output means a regas or a leak, and every garage is booked solid the week it gets hot.
- Clear the scuttle drains and pollen filter.Leaves in the drain channel below the windscreen block airflow to the cabin and cause water to back up into the car. A blocked pollen filter halves the air conditioning's output.
- Check the tyre pressures cold, using the loaded figures.A car packed for a holiday needs the higher figures. Underinflated tyres build heat, which is exactly what you do not want on a hot motorway.
- Look at the tyre sidewalls carefully.Heat finds existing damage. Bulges, cracking and old rubber are far more likely to fail on a hot motorway run than on a damp commute.
- Use a windscreen shade when parked.It keeps the dashboard from reaching temperatures that crack and fade plastics, and it makes the car survivable to get into. Cheap, reusable and genuinely effective.
- Protect the interior surfaces.A UV protectant on the dashboard and a conditioner on leather stops the fading and cracking that sun does over a few summers.
- Wax the paintwork before summer.Ultraviolet is what fades paint and hardens trim. A wax or sealant applied in spring is the protection that carries it through.
- Carry water for people, not just the car.Motorway closures in a heatwave leave people stationary for hours. Water, shade and a charged phone matter more than anything mechanical.
Tips
- Open the windows for the first minute of a journey to dump the hot air, then close them and use the air conditioning. It cools far faster than starting with recirculation.
- Run the air conditioning for ten minutes every couple of weeks all year. It keeps the seals lubricated and stops the gas escaping.
- Park facing away from the afternoon sun where you can — the windscreen is the biggest heat entry point.
Common mistakes
- Leaving a dog in a car with the windows cracked open — A car in the sun reaches dangerous temperatures within minutes and open windows barely slow it. Dogs cannot cool themselves efficiently and heatstroke is frequently fatal.
- Ignoring weak air conditioning until the hot week — Air conditioning systems lose a little refrigerant every year. The one week everyone needs it is the one week no garage has an appointment.
If it doesn't work
Temperature gauge climbs in traffic but is fine moving
Cause: The cooling fan is not cutting in — Fix: Pull over safely, switch off, and get it looked at. Airflow at speed is masking a fan or sensor fault.
Air conditioning blows cool but not cold
Cause: Low refrigerant or a blocked cabin filter — Fix: Change the pollen filter first as it is cheap and easy, then have the system checked for leaks before regassing.
Musty smell when the air conditioning starts
Cause: Damp and bacteria on the evaporator — Fix: Run the air conditioning with the fan high and windows open for a few minutes, replace the cabin filter, and have the system cleaned if it persists.
Dashboard cracking and fading
Cause: Prolonged direct sun — Fix: Use a screen shade and a UV protectant. Existing damage cannot be reversed but it can be stopped from spreading.
Questions people ask
Does air conditioning use much more fuel?
A little, mostly at low speeds. Above about fifty miles an hour, open windows create enough drag that the air conditioning is usually the more economical choice as well as the more comfortable one.
What should I do if the temperature gauge starts rising?
Turn the air conditioning off and the heater to full hot with the fan high, which dumps heat from the engine into the cabin, then pull over safely and switch off. Do not open the coolant cap.
How hot does a parked car actually get?
Far hotter than the air outside, and quickly — the glass traps heat and there is no airflow. It is why leaving a child or animal inside, even for a few minutes on a mild day, is genuinely dangerous.