9 Common Causes of Overheating in Car Engines (& How to Fix them)

While you can push off plenty of problems, an overheating car engine isn’t one of them. Overheating an engine can lead to a car accident and a costly tow truck.

That’s why it’s so important to get to the root of your overheating car engine before you hit the open road.

In this comprehensive guide, we’ll walk you through the nine most common causes of an overheating engine before walking you through how to troubleshoot your engine. By the end, you’ll know exactly what’s wrong with your vehicle and how to fix it! First, let’s take a look at the possible reasons for an overheating engine:

Low coolant levels or broken thermostats are two of the leading causes for an engine overheating. A bad radiator fan may cause the excessive heat to occur only during idle. A broken water pump, or a burst head gasket can cause this problem.

You will see a list of all possible causes down below. We’ll take a dive into the nine most common below before walking you through how to troubleshoot your vehicle.

What causes an engine to heat up?

1. Low coolant, or no cooling

Coolant's primary function is cooling down the engine. So, it’s no surprise that if your vehicle is low or out of coolant, your engine will overheat! Just keep in mind that your vehicle has a sealed cooling system, so if you’re constantly adding coolant, you need to figure out where it’s going.

2. Broken Thermostat

Your vehicle’s thermostat opens and closes as needed to keep your engine at the right temperature. If it’s stuck open or closed, your engine will overheat, which is a significant problem.

The thermostat is located on your engine block/head in a house-like plastic. Refer to your repair manual for the exact location.

3. Broken Water Pump

Your vehicle’s water pump pushes the coolant throughout the engine. Without it, your coolant is sitting stagnant and can’t do its job.

Keep in mind that while your vehicle’s water pump can break, it’s one of the rarer problems, depending on the car model.

4. Broken Fan

Double-check your fan if you notice that your car is overheating while it is idling. Your vehicle's fan circulates air to cool the radiator, making it especially crucial when you are idling.

RELATED : 7 Reasons why your Radiator Fan isn't Coming On

5. Radiator Damaged or Clogged

Your vehicle’s coolant flows through the radiator’s fins to cool down, and if those fins are clogged or blocked, you won’t get enough coolant flow through your engine to effectively cool it down.

A second problem is when debris gets in the way of radiators. This is less frequent, but it can still happen.

Related: Signs and symptoms of a bad radiator

6. Coolant Leak

Although we mentioned low coolant before, an engine that has an internal coolant leak may cause it to heat up even after you have turned off the oil. That’s because if your coolant is mixing with other things, like your oil, nothing is going to cool down as it should.

A coolant leak could cause your engine to overheat quickly.

RELATED : How to fix a coolant leak

7. You can have air pockets in your coolant

It is important to flush all air pockets from your cooling system following a coolant flush. Air pockets will cause your entire system to jam up, and you won’t get any coolant flow.

There will be different instructions depending on your vehicle. To find out what steps are required to flush your coolant, consult your vehicle’s maintenance manual. Overheating can be also caused by coolant pockets.

8. Low Coolant Pressure

Coolant may not build pressure for a variety of reasons. A busted radiator cap or a burst water pump could be the cause. Low coolant pressure can lead to overheating engines.

9. Low oil

Although this is rare, it does happen. Cooling is one of many properties that oil has. Engine components that lack enough oil will cause friction and heat, leading to more heat.

It can heat up if the oil gets too hot. You can check the oil level if you notice your engine heating up.

How to fix an overheated car engine

There are many things that could lead to an engine overheating. However, it is possible to keep the issue from becoming overwhelming by simply KISSing the problem. It’s what every mechanic instructor teaches, keep it simple stupid.

It’s the mechanic’s version of Occam’s Razor. Before you start digging down into the details, it's best to begin with the most common and obvious problems. Check your fluid levels before you try to troubleshoot an engine that is overheating.

1. Check Fluid Levels

Check the oil and the coolant, and if either fluid is low you’ve discovered a critical clue. It is possible to top-off the fluid, and then see if your problem disappears. However, both the coolant and oil systems are sealed so you will need to investigate if there are fluid leaks.

2. This will force the system to work.

After the engine has cooled completely, you can use a radiator tester to check for leaks and then place it on top. You can use this handy device to test the system and check for other problems. If you don’t own one, don’t worry, most part stores like AutoZone will let you rent one for free.

First, it will make it abundantly obvious if you have a leak – whether internal or external. The pressure in your system must be maintained. If it doesn’t, you have a leak somewhere.

This tool can be used for that purpose.

Check the thermostat next. You can check this by checking the lower radiator hose’s temperature (or upper if that’s the output of the thermostat). It is possible that the thermostat has a problem if it's still cold at the time the car overheats.

Remember that if you have a broken electric thermostat, you will usually have a check engine light – but that’s not always the case. Take a look at the fan if your thermostat is functioning properly. Turn on your engine and open the hood. The fan should turn on eventually. If it doesn’t, you either have an electrical problem with the fan or a busted fan.

You must also ensure that coolant flows are maintained in the engine. This requires some expertise and you may need to consult a mechanic for a more thorough diagnosis.