Car overheating: is it your thermostat, coolant, or radiator?

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3 min read

We know, we know…your car is smoking hot, but is it so hot it’s literally smoking? If white clouds are pumping out from under the hood then that’s a surefire sign that your car has overheated. Other signs are the engine temperature gauge spiking, or a bad smell coming out of the engine. None of these are signs to ignore.

Nothing puts a downer on a summer road trip like your car pulling its best Hogwarts Express impression. But when the mercury rises, so do the chances of your car starting to steam. So what should you do if your car overheats?

Let’s take a look at the main causes and how to fix it.

A warning—wait a good 15 minutes for your car to cool down before popping the hood, and wear gloves before you start checking the engine. DO NOT remove the radiator cap until the car cools down.


A faulty thermostat is a common cause for a car to start overheating. This is a valve that controls the flow of coolant around the engine. When the engine starts to get too hot, the valve will release more coolant. If the valve breaks, it could fail to open, meaning your engine will simply get hotter and hotter. The fix should be relatively inexpensive. Simply replace the thermostat—you could even do it yourself.


If the coolant levels get too low (or run out completely) that can be another common cause for a car to overheat. It could be running low because of a leak, so check for any puddles under your car. Another problem can be using the wrong type of coolant, so have a flick through your user manual to make sure you’re using the correct formula for your engine. Once you’ve done your checks, open the radiator cap and top up the coolant with a 50/50 mix of water and antifreeze, and you should be good to go.


A faulty radiator fan can also cause a car to overheat. This could be due to a number of issues. It could be a blown fuse, or a broken motor. Or the coolant could be too low, meaning the fan has to go overdrive to keep the engine cool. If you’ve checked (or topped up) the coolant and it’s still not helping, you may want to call a mechanic to help. A radiator fix or replacement can be tricky to handle and will likely cost you too.

engine oil

Engine oil keeps your engine components lubricated, but it also plays a role in keeping the engine cool. If your car is overheating, it’s worth checking the oil levels as it may require a top up. Again, check for leaks—if you spot puddles of engine oil under your car, a more serious repair might be needed.

Oftentimes, your car overheating isn’t a sign of anything serious. It’s just a case of topping up the coolant. But sometimes it’s a clue that something major is malfunctioning, and the fix requires a trip to the mechanic.

If overheating is a persistent problem—and not worth the money and hassle to fix—it might be a good moment to cash in your old car. At Peddle, we’d be happy to give you a cash offer in minutes no matter what condition your car is in.