Car overheating: stop first, diagnose second
Overheating is the one fault where the right response comes before any diagnosis. Switch the engine off as soon as it is safe to do so. Allow it to cool completely. Do not continue driving an overheating vehicle because serious engine damage may occur.
Once the engine is completely cold, and only then, the checks below are safe to make.
Common symptoms
- Temperature gauge climbing towards or into the red
- Steam or a sweet smell from the bonnet
- Coolant level dropping, or puddles under the car
- Heater blowing cold when the engine is hot
- A coolant or temperature warning light
Simple checks you can do safely
- 1
Wait until the engine is completely cold
Do not open the coolant or radiator cap while hot — pressurised coolant can cause serious burns. Keep hands, clothing and hair away from fans and belts, which can start without warning.
- 2
Check the coolant level in the expansion tank
Cold engine only. A level below minimum tells you coolant is being lost somewhere; it does not tell you where.
- 3
Look for evidence of the leak
Dried white or coloured residue on hoses, around the radiator, or under the car. Do not restart or run an overheating engine just to look for leaks.
- 4
Check the radiator and its airflow
Look for obvious damage or a front face packed with leaves and debris. Both reduce cooling.
- 5
Note when it overheats
In traffic only, at motorway speed only, or all the time. Overheating only when stationary often points towards airflow and cooling fans.
Do not buy or replace parts until the fault is confirmed, and never work under a vehicle supported only by a jack.
Warning signs: do not drive
- The temperature gauge is in the red — stop as soon as it is safe and switch off
- Steam is coming from the bonnet
- You are losing coolant repeatedly
- Arrange an inspection or recovery rather than driving "just a short distance"
AutoFix AI treats overheating as a stop-driving condition automatically, and will not offer procedures that involve a hot engine.
Common questions
Why is my car overheating?
Coolant loss, an airflow or cooling fan problem, a thermostat stuck closed, or a water pump issue are the usual areas. When it overheats — in traffic only, at speed only, or always — is the most useful clue.
Can I drive a short distance if my car is overheating?
No. Switch the engine off as soon as it is safe to do so and allow it to cool completely. Do not continue driving an overheating vehicle because serious engine damage may occur. Arrange an inspection or recovery instead.
Where is my coolant disappearing to?
Coolant does not get used up in normal running, so a falling level means it is leaving somewhere — a hose, the radiator, a pump seal, or internally. Look for dried residue and puddles once the engine is completely cold.
Can I open the radiator cap to check?
Not while the engine is hot. Pressurised coolant can cause serious burns. Wait until it is completely cold, and keep hands, clothing and hair away from fans and belts, which can start without warning.
These describe what a symptom commonly suggests. They are not a confirmed diagnosis of your vehicle.
Related guides
Still not sure what's wrong?
Describe the symptoms, add photos, video or an engine sound, and work through the likely causes with the checks that separate them.
Diagnose my car