Car Overheating: Causes and What to Do at the Roadside
Written by Petro Olekhnovych, mobile mechanic in Aylesham, Kent
If your car is overheating, pull over somewhere safe as soon as you can, switch off the engine and let it cool for at least 30 minutes. Never open the radiator or coolant cap while the engine is hot. Do not keep driving an overheating car, because the RAC warns this can cause lasting engine damage.
How to tell your car is overheating
Most cars warn you in one of two ways:
- A temperature gauge climbing towards the red.
- A temperature warning light, usually a small thermometer symbol.
The AA says a yellow or amber temperature light probably means the coolant level is low, while a red light means the engine is overheating. Many modern cars have no gauge, so the warning light may be your only clue. Steam from under the bonnet is another sign.
If you want to understand the warning light itself in more detail, read our post on the engine temperature warning light.
What to do at the roadside, step by step
These steps follow RAC advice and the Highway Code.
- Turn the heater to full heat. The RAC suggests this as a temporary measure while you find somewhere to stop, because it draws heat away from the engine.
- Pull over somewhere safe. On a motorway, the Highway Code says to leave at the next exit or pull into a service area if you can. If not, use an emergency area or hard shoulder and stop as far left as possible.
- Hazard lights on, engine off.
- Get everyone out on the left-hand side, away from traffic, wearing hi-vis if you have it. The Highway Code says that if you cannot get out safely on a motorway, stay in the car with your seat belt and hazards on, and call 999.
- Open the bonnet carefully if you can. The RAC warns it may be very hot from the steam.
- Wait. The RAC says at least 30 minutes, and an hour or two is safer.
Never remove the radiator or expansion tank cap while the engine is hot. The system is pressurised and the AA warns you could be scalded by a sudden release of hot water. Once it has fully cooled, open it slowly with your hand covered.
Engine problem or belt due?
Timing belts, water pumps, coolant and fault finding done at your door.
WhatsApp for a free quote Call 07563 350335
Labour £30 to £50 per hour depending on the job. Send your reg number and we will reply with a price before any work starts.
Should you top up the coolant?
Once the engine is cool, check the coolant expansion tank. The AA says the level should sit between the min and max marks, and it should be checked only when the engine is cold.
- If it is low or empty, top up with the coolant type in your handbook. The AA says different antifreeze types do not mix well. Look under the car for puddles or drips, which suggest a leak.
- Plain water is an emergency measure only, to get you to a garage. The AA warns that a weak mix over winter can freeze and damage the engine. The RAC says never pour cold water into a hot engine.
- If the level is fine, the RAC says the cause is likely mechanical and needs a professional.
If the warning comes back after topping up, the RAC advises getting the car checked as soon as possible. If it comes back quickly, stop again and call for help rather than driving on.
Common causes of a car overheating
The AA says a seized cooling fan is the most common cause of initial overheating. Other causes the AA and RAC list include:
- Low coolant, from a leak or the engine using coolant. The AA says it is not normal for the level to drop. Our post on coolant leak signs covers this.
- A faulty cooling fan. The AA says it switches on when the car is stationary or the engine gets too warm. A fan fault often shows up as overheating in traffic.
- A faulty thermostat.
- A failing water pump, which can stop coolant circulating. See our guide to water pump failure symptoms.
- A blockage in the cooling system.
- Low engine oil, according to the RAC.
The RAC adds that hot weather can make an existing problem worse. Sometimes overheating points to a more serious engine fault.
What happens if you keep driving?
The AA says overheating is the most common cause of head gasket failure. Signs of a failed head gasket include white exhaust smoke, a sweet smell from the exhaust, a milky deposit on the dipstick or oil filler cap, and loss of power. The AA does not recommend driving with a blown head gasket.
The RAC says overheating should not cause lasting damage if it is dealt with quickly and safely. Driving on is what turns a small repair into a big one.
How to help prevent overheating
- Check your coolant level regularly with the engine cold. The AA suggests about every two weeks.
- Watch the temperature gauge or warning lights, especially in traffic and hot weather.
- Never ignore a coolant level that keeps dropping.
- Have the cooling system checked as part of regular servicing. Intervals vary by car, so check your handbook.
How we can help
We are a mobile mechanic based in Aylesham, covering Canterbury, Dover, Deal, Sandwich, Folkestone and the villages in between. Once your car is safely stopped, we can come to you at home or work, find the cause of the overheating and tell you what it needs. We also replace water pumps and do interim and full servicing.
Labour is £30-£50 per hour depending on the job, parts are extra, and we agree the price on WhatsApp before starting. You can also book an appointment.
Frequently asked questions
How long should I let an overheated engine cool down?
At least 30 minutes, according to the RAC. An hour or two is safer before opening anything.
Can I drive a short distance with the engine overheating?
No. Stop as soon as it is safe and switch off. Driving on risks serious engine damage.
Why does my car only overheat in traffic?
When you are stationary, there is no airflow through the radiator. The AA says the cooling fan takes over then, so a faulty fan often shows up in traffic.
Is it OK to put water in my coolant?
Only in an emergency to reach a garage. Top up with the right coolant mix as soon as you can.
Need help? Send a WhatsApp to 07563 350335 with your car’s make and model and we’ll come to you.
Engine problem or belt due?
Message us on WhatsApp with your reg and postcode for a price before any work starts.
WhatsApp for a free quote Call 07563 350335
Labour £30 to £50 per hour depending on the job. Send your reg number and we will reply with a price before any work starts.
