So, what does it mean when a car overheats? When you check the temperature gauge on your dashboard, you’ll notice there are two letters on it – a C and an H. You can check out this post: what does the c and h mean in a car for a deeper explanation. However, for the sake of this post, the letters simply mean ‘Cold’ and ‘Hot’ respectively.
In between the letters C and H, there’s a little ‘plastic-like’ gauge that moves up and down. Ideally, this gauge is always supposed to be somewhere in the middle of the letters whenever your car has been driven around for a while.
Overheating occurs whenever this gauge gets to the letter ‘H’. At this point, it means your engine is hot due to a malfunction of any of the cooling systems.
Sometimes this overheating stays constant but at other times, it goes back to normal on its own after a while. In this post, we’ll be taking you through the major reasons for a car overheating and then going back to normal.
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Major Reasons Why A Car Overheats Then Goes Back To Normal
Obviously, at this point, your first instinct would be to pop the hood open and see what’s happening underneath. But I’ll have to warn you. Do not open the hood when the car is still hot. Just turn off the ignition and give the car enough time to cool off. It doesn’t matter how late you are for that appointment. Just book a cab or something.
So, with that said, here are some of the major reasons why a car would overheat:
1. Low Coolant
When the engine is cold, take the radiator cap off and look inside. In most cases, it will be dry. So the next thing to do is to pressure test the system to check for leaks. If you’d like to do this yourself, use a pressure leak testing system. You can get a used one for around $30 or a new one for around $70.
Just hook it up to the radiator and then pump up the pressure. If there’s a leak, you’ll see the coolant come right out of the radiator. This tells you that the radiator is just full of holes.
Now, this case is pretty easy. There’s a hole in the radiator. But if it was more complex, you watch the pressure on the gauge and see if it starts to move down. Pump it up to 16Ibs pressure and watch the gauge. If starts dropping a bit rapidly, you know there’s a leak and you have to find where the squirt is coming from.
But let’s say you pressure-tested it and there weren’t any leaks at all. What do you do next?
Well, one thing you need to know is that the radiator cap is supposed to hold pressure in, so if they’re worn and rusty, you might just need a new radiator cap.
Now there are machines that test radiator caps but hey, these caps are really cheap so just go buy another one and stick it on. You can check out these bad radiator symptoms to get familiar with things you should be looking out for before committing to any changes or repairs.
2. Faulty Cooling Fans
Now if the radiator fix doesn’t solve the problem of overheating, the next thing to check is the cooling fans. So start the car up and turn up the AC to full blast. Then go back under the hood and check the cooling fans to see if they’re working. Usually, you’ll see the left and right fans turning.
If the fans aren’t working, there won’t be enough air sucked through the radiator and it will overheat. And when they don’t work, check the fan motors. They often burn up.
To check to see if the motors are out, just get a little jumper wire and stick one end on the positive cable of the battery and stick the other end on the red cable that feeds the motor. If the fan doesn’t start spinning, you’ll know the motor is burned out.
3. Bad Thermostat
Let’s say the fans are working fine, you might have a bad thermostat. The thermostat close to the engine warms up and when it gets hot, they’re supposed to open up. And sometimes they stick.
Most thermostats are pretty easy to get to. On a Toyota (I use a Toyota), you just follow the bottom radiator hose and you’ll find the thermostat housing back there. It just has a bolt on the top and a bolt at the bottom. You pull it out and replace the thermostat. And then you better hope a new thermostat fixes your overheating problem because if it doesn’t, then you have either one of two rather expensive problems.
4. Radiator Unable to Dissipate Heat
Now, these modern radiators are made of plastic and aluminum which often corrode inside and stop dissipating heat. They don’t leak and they look perfectly fine. But, they just can’t get rid of the heat. This can result in a situation where your car temperature gauge goes up and down while driving.
If this is the case, then you’d need to spend some money on a new radiator and you better hope that fixes the problem because the only other issue could be a bad head gasket.
5. Bad Head Gasket
In this case, you’d have to tear the engine apart and that can cause well over $1,000 on most modern cars. So before you tear the engine down, it’s a good idea to conduct a combustion leak test on it to make sure the head gasket is leaking.
The combustion leak test is a simple test where the blue liquid is put into a tube and then the engine is run to see if the blue turns yellow. If it does, you’ve got a head gasket leak and you’d have to change it.
So next time when your car starts overheating, don’t get mad. Just get under the hood, and take the following steps listed here to diagnose your coolant level, cooling fans, thermostat, radiator, and head gasket. Most of these fixes are things you can do yourself. However, if you’re not feeling very confident, We’d advise you to take your car to an auto mechanic to have a look.
Ugo is a passionate car enthusiast with a Bachelor of Electrical and Electronics Engineering degree and hands-on experience in troubleshooting and fixing automobiles.
I combine my electrical and mechanical engineering knowledge with practical skills to address car-related issues.
My love for cars and dedication to educating others led to the creation of Fixandtroubleshoot.com!