Temperature light on or steam? Pull over now
Stop as soon as it's safe, ideally clear of traffic, and switch off. RACQ says even a short extra drive can greatly increase the damage. Don't open the bonnet while there's steam, and never take the radiator or coolant cap off a hot engine: pressurised coolant and steam can burn you badly. If you're stuck on a busy road, get everyone out on the side away from the traffic, and call roadside assistance if you have it. If anyone is hurt or in danger, call 000.
What to do once you've stopped
Leave the bonnet closed
The NRMA's advice is to keep it shut and let the engine cool. Steam escaping near your face is the danger, and the engine doesn't need you to look at it yet.
Wait longer than you think
The NRMA says it can take over an hour. RACQ says cooling completely could take several hours. A cool engine bay isn't the same as a cool engine, so don't rush it.
Look under the front of the car
From where you're standing, see if there's fluid on the ground. A green, orange or pink puddle means a coolant leak. Note it for the mechanic.
Don't pour cold water in
RACQ says refilling a hot engine with cold water can cause major damage. Once it's fully cold, you can look at the coolant bottle, but adding water still doesn't fix anything.
Get help moving it
If the temperature went high, we'd have it towed or seen where it sits, not driven. The NRMA says the car goes to a repairer if engine damage is suspected or it can't be fixed at the roadside.
What does the temperature light mean?
The temperature warning light looks like a thermometer in waves. RACV says it means the engine is too hot or too cold. A red one means too hot, stop. On some cars a blue version shows while the engine warms up, and that one's normal.
Many cars also have a gauge. Learn where the needle usually sits, about the middle on most cars. If it creeps higher than normal, that's the early warning, and you've got time to get off the road properly. Some newer cars have no gauge, only the light, so treat that light as your first and only warning.
Why does a car overheat?
| What you might notice | What the repair usually is | |
|---|---|---|
| Low coolant from a leak | A puddle, a falling level, a sweet smell. The NRMA points to cracked radiators and split hoses. | Fix the leak, refill and bleed the air out. |
| Thermostat stuck shut | The gauge shoots up within minutes of starting. | A new thermostat. It's a valve that lets coolant through once the engine's warm. |
| Water pump failing | Noise or a drip from the front of the engine, overheating at any speed. | A new pump, sometimes with the timing belt. |
| Fan not working | Fine on the highway, hot in traffic or at the lights. | The fan, its relay or a sensor. |
| Blocked radiator | Slowly hotter over months, worst on hot days or towing. | A flush or a new radiator. |
| Blown head gasket | Vanishing coolant, white smoke, milky oil. | See blown head gasket. |
Why it often happens on the hottest day
RACQ says poorly maintained cooling systems, and ones with even minor leaks, are more likely to give up under the extra pressure of hot weather. An ageing hose can hold on all winter and split on a stinking hot January afternoon in traffic. Towing a van or heavy loads uphill adds to it.
That's also why a quick check helps. The NRMA suggests looking at the coolant level every time you refuel, with the engine cold, and having any drop checked.
What will the mechanic do?
First they find why it overheated, then check what it cost the engine. Expect a pressure test on the cooling system, a look at the fan, thermostat and pump, and a check for exhaust gas in the coolant to rule out the head gasket.
Tell them how high the gauge went, how long you drove after it rose and whether you topped anything up. RACQ warns that damage may not show for days, weeks or even months after an overheat, so a car that seems fine after a top-up still deserves a proper look. A written estimate should separate the repair for the cause from any further work the checks turn up. Most mechanics deal with cooling faults regularly. If the head gasket comes into question, ask for one who does engine work.
What you can do, and what's the mechanic's job
You can
- Stop, switch off and wait for a fully cold engine.
- Check the coolant bottle level when it's cold.
- Notice when the gauge rises: traffic, hills, highway, towing.
Leave to the mechanic
- Opening the cooling system and bleeding air out of it.
- Pressure testing, and checking the head gasket.
- Replacing the pump, thermostat, fan or radiator.
If it were our car
We wouldn't drive it again until we knew why it got hot, even if it cooled down and seemed fine. We'd send the job with a note saying how high the gauge went, and ask whether a mobile mechanic can see it where it sits or whether it needs a tow. A cooling repair done now is usually far smaller than the engine repair it can head off.