Pull over before the gauge reaches red
When a car’s temperature gauge climbs, the heater trick buys a few minutes at most. Pull over, switch off, wait, and never open a hot cap.
From people’s advice and experience shared online, including a mechanic and people who limped a car to a shop; the steps are checked against AAA in the US and the RAC in the UK, October 2026.
The temperature needle is climbing, or a red light has come on, and you are in traffic on a hot day. Pulling over means being late and being stranded. You may have heard that turning the heater on will fix it.
Pull over as soon as it is safe, turn the engine off, and do not keep driving.
This page is for petrol and diesel cars. If your problem is a hot cabin, not a hot engine, or you drive an electric car, it is not the page you need.
What to do, in order
If you can stop right now, stop. If you cannot, because of traffic or a motorway, AAA says to turn the air conditioning off and the heat on while you look for a place to pull over. Then:
- Pull over where it is safe, turn off the engine and put the hazard lights on. The RAC says on a motorway to leave at the next exit or pull into a service station.
- Get everyone out and away from the road.
- Do not open the hood (the bonnet, in the UK), or touch the front of the car, for at least the minimum at the top of this page. AAA says about 20 minutes, the RAC at least 30; longer is fine.
- Once it is cold, check the coolant level in the reservoir. The RAC says to top it up with coolant, or a mix of water and coolant, and to look under the car for leaks if the reservoir is empty.
- Do not drive on. The RAC says never to continue driving an overheated car, and AAA says adding coolant may give temporary relief but a professional has to diagnose the cause. Call your breakdown or roadside service.
The heater trick, and what it is
Many people say turning the heater on full blast helps a car that is overheating, because the heater works as a small second radiator that draws heat out of the coolant. Many of them also say it is temporary and only for minor overheating. AAA gives it for the same narrow situation, when you cannot stop right away, and tells you to turn the air conditioning off first.
Whether it helps depends on what is wrong. Some people say it only works if the engine is running and coolant is flowing through the heater core, and another that if the radiator is cracked it lasts only until the remaining fluid is gone. One person points out that if the thermostat is stuck closed, coolant flow stops and the heater does nothing. One person who works as a mechanic calls it one of the worst pieces of advice, because it masks the problem while the engine cooks inside and risks head gasket failure; the person who wrote the tip answered that it has saved them thousands in repairs. One person describes using it to get to a store for coolant when the car was running low. One person reads a heater that blows no hot air as a sign of low fluid, an air bubble, a thermostat fault or a blocked heater core.
The way to hold both is the way AAA does: the heater is a bridge to the place you stop. Stopping costs a delay; the RAC says driving on could cause lasting damage to the engine.
What the gauge can hide
One person says that many modern cars have only a warning light, not a gauge with a needle, which makes severity harder to judge. One person says some older cars had sensors that could show a low temperature even with an empty radiator. One person points out that a car with no coolant circulating can run hot even on a cold day. A warning light that comes back on could be a sign of a problem with the cooling system, according to the RAC, which says to get the car seen at a garage as soon as possible.
Who this page is not for
An electric car has a different cooling system and no engine to overheat in the same way, and this page does not cover it. Nor does it help you work out what is wrong with your car; the manual and a mechanic are the next step.
Common questions
I’m in traffic and can’t stop yet. What do I do?
AAA says that if you cannot pull over right away, turn off the air conditioning to ease the load on the engine, then turn on the heat, and that this will make the car uncomfortable but can help the engine cool slightly while you drive. That is a bridge to a place to stop, not an alternative to stopping. Many people say the same about the heater, and say it is temporary and for minor overheating. Once you can stop safely, pull over and switch the engine off.
Should I leave the engine idling to keep the coolant moving?
Both AAA and the RAC say to pull over and turn the engine off. People disagree about it. Many people say to switch off at once to stop the heat building and prevent damage such as a warped head or a blown gasket. One person argues that for mild overheating, idling with a reduced load and the heater on keeps the water pump moving coolant, while switching off stops it and can make the block hotter. One person points out that running the fan after you switch off does little, because the water pump stops with the engine. The idling argument rests on how the water pump works, and it is a reason to know your car; it is not a reason to override what both organisations say.
Can I pour cold water on it to cool it?
Not on a hot engine. Some people warn that cold water poured over a hot engine block, or into a hot radiator, can crack the block or cause severe burns from steam, and the RAC says to avoid pure cold water on a hot radiator because it can damage the engine. People disagree about how much damage it does: one person calls cracked blocks an old wives’ tale, and a mechanic replied that it depends on the water temperature, the amount, and whether the engine was already damaged. One person says they have never seen a cracked block from it, but have seen head gaskets and water pumps fail from rapid cooling, for example at a car wash. Waiting for it to cool by itself costs nothing.
Can I top up with plain water? What about stop-leak?
The RAC says that once the engine is cold you can top up with coolant or a mixture of water and coolant. One person says plain tap water will do as an emergency measure, to protect the engine; another warns that using tap water in place of proper coolant can cause internal corrosion. One person warns against stop-leak powders and the egg-in-the-radiator hack, saying they clog the system. One person also warns that on some cars the overflow bottle is itself pressurised, so the safety line above covers it too. If the reservoir is empty, the RAC says to look under the car for leaks.
My car has been fine for years and the gauge just spiked. Is it the same?
It is a case for stopping. One person says the heater trick only helps mild overheating or a car that gets hot idling in hot weather; if a car that has always been dependable abruptly shoots into the red, they say, that points to a serious failure such as low coolant or no circulation, and a small extra radiator will not help, so pull over and switch off. The RAC says never to continue driving an overheated car, because it could cause lasting damage to the engine.
Questions this step helps with
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