Car overheating: what to do, common causes and how to prevent it
If your car starts to overheat, pull over as soon as it is safe, switch off the engine, and let it cool for at least 30 minutes before you check anything. Never open the coolant cap on a hot engine, because the system is under pressure and can spray scalding coolant. If the temperature gauge is in the red or steam is rising from the bonnet, do not carry on driving.
This guide covers the warning signs, exactly what to do step by step, what not to do, the most common causes, and how to avoid it happening again.
Last updated 29 September 2026. The steps follow advice from the RAC and Green Flag, and your handbook takes priority if it differs.
Key takeaways
- Warning signs include a rising temperature gauge, a thermometer warning light, steam, a sweet smell and a cold heater.
- Pull over safely, switch off the engine and wait at least 30 minutes before opening the bonnet or checking coolant.
- Never open the coolant cap on a hot engine, and never pour cold water on it.
- The most common cause is low coolant from a leak, but faults with the thermostat, water pump, radiator, fan or head gasket can also be to blame.
- Do not keep driving. Overheating can cause serious and expensive engine damage.
- Check the coolant level monthly, when the engine is cold, to prevent it.
In this guide
- How do you know your car is overheating?
- What to do if your car overheats, step by step
- What not to do
- What causes a car to overheat?
- Why does my car overheat in traffic or hot weather?
- What damage can overheating cause?
- How to stop your car overheating
- When to call a breakdown service
- What about hybrid and electric cars?
- Frequently asked questions
- Sources and further reading
How do you know your car is overheating?
- The temperature gauge climbs into the red, or a thermometer-shaped warning light comes on
- Steam or smoke coming from under the bonnet
- A sweet smell, which can be leaking coolant
- Ticking, knocking or bubbling noises from the engine
- A noticeable loss of power
- The heater blowing cold air, which can mean the coolant level is low
- A puddle of green, pink, orange or blue liquid under the car
The RAC says a temperature warning light can be your first sign of low coolant. Treat it seriously, because an overheating engine can be damaged within minutes.
What to do if your car overheats, step by step
- If you cannot stop straight away, turn off the air conditioning and turn the heater and fan up to full. This draws some heat away from the engine into the cabin. It is a short-term measure only.
- Pull over as soon as it is safe. Put your hazard lights on and stop somewhere you can get out safely.
- Switch off the engine. Follow your handbook if it gives different advice for your model.
- Get everyone to safety. Use the doors furthest from the traffic, and on a motorway get out of the left-hand doors and stand behind the barrier if it is safe.
- Do not open the bonnet straight away. Steam and hot metal can burn you. Wait until the steam has stopped.
- Wait at least 30 minutes. The RAC advises letting the engine cool for at least 30 minutes before you carry on.
- Check the coolant level when the engine is cold. Look at the reservoir, which has minimum and maximum marks. If it is low, top it up with the coolant type your handbook specifies.
- If the warning comes back, or you cannot find the cause, do not keep driving. Call a breakdown service.
If you have to use plain water in an emergency to get to a garage, remember it dilutes the coolant, so have the system checked and the mixture corrected soon afterwards.
What not to do
- Do not open the coolant cap on a hot engine. The system is under pressure, and even loosening the cap slightly can release a spray of scalding coolant.
- Do not pour cold water on a hot engine. A sudden change in temperature can cause parts to crack.
- Do not keep driving to try to reach home or a garage. It risks serious engine damage.
- Do not restart the engine until it has cooled and you have found and dealt with the cause.
- Do not ignore it if it seems to fix itself. An overheating engine usually points to an underlying fault that will come back.
What causes a car to overheat?
| Cause | Typical signs | Usual fix |
| Low coolant or a leak | Warning light, sweet smell, puddles, cold heater | Find and repair the leak, then top up with the right coolant |
| Thermostat stuck closed | Engine overheats quickly after starting, one radiator hose hot and the other cool | Replace the thermostat |
| Failed water pump | Coolant leak near the front of the engine, squealing or grinding noise | Replace the water pump |
| Blocked or leaking radiator | Overheating, especially under load, visible leaks or corrosion | Flush, repair or replace the radiator |
| Faulty radiator fan | Overheating in traffic or when stationary, but fine at speed | Replace the fan or its relay, fuse or sensor |
| Broken or loose drive belt | Squealing, battery or steering warning lights | Replace the belt |
| Faulty coolant cap | Coolant escaping, system not holding pressure | Replace the cap |
| Blown head gasket | White exhaust smoke, milky oil, constant coolant loss | Head gasket repair, which is a major job. See what UK drivers pay for a head gasket repair |
Why does my car overheat in traffic or hot weather?
Overheating in queues or on hot days often points to a cooling fan that is not working, a partly blocked radiator, or a cooling system that is already low on coolant. Air conditioning puts extra load on the engine, so turning it off can help in a pinch. If your car only overheats when you are stationary, mention that to the garage, because it narrows down the cause.
What damage can overheating cause?
Running a car that is overheating can warp the cylinder head, blow the head gasket, crack the engine block or even seize the engine. The RAC warns that continuing to drive an overheated car can cause lasting damage and cost far more in the long run than stopping straight away. That is why stopping and calling for help is almost always the cheaper choice.
It is also worth knowing what your insurance covers. Damage caused by a lack of maintenance may not be covered, so read whether engine failure is covered by car insurance.
How to stop your car overheating
- Check the coolant level once a month, with the engine cold, and before long journeys. Our guide explains why engine coolant matters
- Use the coolant type in your handbook. Do not mix different types
- Watch the temperature gauge, and act early if it starts to rise
- Fix small leaks and replace worn hoses and belts before they fail
- Have the cooling system checked at every service, and ask when your coolant is due to be replaced. See what a car service includes
- Do not ignore warning lights. See our dashboard warning lights guide
- Before a hot-weather road trip, run through the checks in our summer road trip checklist
When to call a breakdown service
- The temperature gauge is in the red or steam is coming from the engine
- The warning light returns after you have topped up the coolant
- You cannot see a cause, or you find a leak
- You are in an unsafe location, such as a live lane, a hard shoulder or a busy road
- You are not confident checking under the bonnet
See what to do when your car breaks down and why breakdown cover is a must-have for every driver. You can also find out more about Rooster Breakdown Assist.
What about hybrid and electric cars?
Electric and hybrid cars have cooling systems too, including for the battery and motors, and they can show warnings if something is wrong. If a warning appears, stop safely, switch off, and follow the handbook or call for help. Do not try to open or work on high-voltage components.
Frequently asked questions
Can I drive with the temperature gauge in the red?
No. Pull over safely and switch off the engine. Driving on risks lasting engine damage, including a blown head gasket or a warped cylinder head.
How long should I wait before checking the coolant?
The RAC advises letting the engine cool for at least 30 minutes. The reservoir and hoses should be cool enough to touch before you open anything.
Can I use water instead of coolant?
In an emergency, plain water can get you to a garage, but it dilutes the coolant and reduces its ability to protect against boiling and freezing. Have the mixture corrected soon after.
Why is my heater blowing cold air when the engine is hot?
It can mean the coolant level is low, so there is not enough hot coolant reaching the heater. Stop and check once the engine has cooled.
Does white smoke mean a blown head gasket?
It can. White smoke from the exhaust, milky oil and constant coolant loss are all signs of a possible head gasket failure, so get it checked by a garage as soon as possible.
Will breakdown cover help if my car overheats?
Most breakdown policies cover roadside assistance for mechanical failures such as overheating, but cover levels differ, so check your policy.
Why does my car only overheat in traffic?
Often it is a cooling fan that is not working properly, a partly blocked radiator or low coolant. Tell the garage when it happens, because it helps them find the cause.
How often should I check my coolant?
Once a month with the engine cold, and before long trips or hot weather. Your handbook shows where the reservoir is and which coolant to use.
Sources and further reading
- RAC Drive: What should I do if my car is overheating?
- Green Flag: Car overheating, expert advice to prevent and fix issues
About this guide: Rooster is a UK car insurance provider. This guide is general information for UK drivers and is not a substitute for your car’s handbook or advice from a qualified mechanic or breakdown provider. If you are unsure at any point, call for help.
Protect your wallet as well as your engine. Download Rooster and start saving.
