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Car Cooling System: What is it and How it Works?

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Car Cooling System: What it is and How it Works
Car cooling system is what’s stopping our car from overheating every few minutes!

Our car engines is like a war zone.

Explosions everywhere.

When active, it can set off 4000 controlled explosions per minute. That’s enough heat to absolutely destroy your engine within minutes.

How crazy is that?

That, is exactly why we need a car cooling system.

By the end of this article, you will understand what is a car cooling system, how it works and how to maintain it so it keeps your engine cool all day every day.

Feel free to skip ahead to any of the sections below that you find interesting.

P.S. Car cooling system and engine cooling system, they’re the same thing.

What is car cooling system?

The image shows the parts of a car cooling system in a schematic form. The caption of the image is "Car cooling system is also called engine cooling system for a good reason. It cools the engine."
Car cooling system is also called engine cooling system for a good reason. It cools the engine.


Image by greenfire007 (CC BY 3.0).


Car cooling system maintains our engine temperature. Huge emphasis on the word – “maintains”. It doesn’t just keeps our engine cool, it also keeps it warm enough so that it operate efficiently and cleanly.

Doesn’t matter if it’s summer or winter, our car engine should operate between 90 and 110 degree Celcius.

Here’s why.

If the engine temperature is freezing cold, the fuel won’t burn cleanly and we will suffer in terms of fuel economy and emission. On the other hand, if the temperature is too high, it will start to damage our engine parts.

Car cooling system haven’t changed much since the early days. Sure, it’s gotten a lot more efficient and eco-friendly. But all in all, it still works by circulating coolant throughout the engine to absorb the heat, cool it down with radiator, and then circulate back into the engine again.

What are the components of our car cooling system?

Our car cooling system are made up of many parts, but we can always boil it down to these 7 main components.

  • Radiator.
  • Coolant.
  • Radiator Cooling Fans.
  • Pressure Cap & Reserve Tank.
  • Water Pump.
  • Thermostat.
  • Hoses.

Component #1: Radiator

Radiator are layered aluminium tubes that maximizes its surface area. It can be found at the front of our car.
Radiator are layered aluminium tubes that maximizes its surface area. It can be found at the front of our car.


Image courtesy of Nick Ares (CC BY-SA 2.0), edited by D S Auto.


A radiator is a type of shell-and-tube heat exchanger. It’s primary function is to exchange heat energy from one medium to another to get either a cooling or heating effect.

In a tropical country like Malaysia, it’s more common to find them in automotive applications. But if you have the opportunity to travel to other countries with colder climate, you can see them in the house too! Radiator can help to heat up the houses during winter time.

But you may be wondering…

Whenever something hot is in contact with something cold, it exchanges heat. So, why do we need to bother installing a radiator?

That is because radiators are optimized for heat exchange.

Inside a radiator, you will find aluminium tubes that are arranged in parallel. It bends back and forth like a “S” shape so that you can fit a really long tube inside a smaller box. This way, you get a larger surface area.

When surface area is higher, more coolant is in contact with the surrounding air, and therefore improving the heat exchange rate.

Component #2: Coolant

Coolant is a mixture of antifreeze, distilled water, and additives.
Coolant is a mixture of antifreeze, distilled water, and additives.


Image courtesy of EvelynGiggles (CC BY 2.0)


Coolant is usually a red, orange, or green fluid that we add into our radiator. Its purpose is to circulate around the engine and takes heat away from it. It is made from 50% antifreeze, 50% distilled water, and small traces of additives.

Antifreeze are chemicals like ethylene glycerol or propylene glycol which alters the freezing and boiling point of the water. Without it, the fluid boils so easily that you will start seeing water vapor coming out from your car’s bonnet.

Distilled water is used in coolant because they have naturally high heat capacity, which makes it a suitable heat-transfer medium. And the best part? They’re FREE (well almost).

Different assortments of additives are also added to inhibit rusts, prevent foaming, and etc.

When you add these three things together, they become the coolant that we use in our car cooling system.

Component #3: Radiator Cooling Fan

Radiator fan drives airflow towards the radiator.
Radiator fan drives airflow towards the radiator.

Radiator fans can be either…

  • Mechanical
  • Electrical

These two types of radiator cooling fan performs the same function, but a mechanical radiator fan is driven by engine belt, while an electrical radiator fan is a DC motor that is powered by vehicle’s electrical system.

It usually has 4 to 6 blades fan that spins rapidly to draw air flow through the radiator to cool the coolant.

If you really want to drill down to the nitty gritty details, it actually cool the engine too (although not a lot). Majority of the cooling is still done by heat transfer through the coolant.

Component #4: Pressure Cap & Reserve Tank

Pressure cap are found on top of our car radiator.
Pressure cap are found on top of our car radiator.

Pressure cap helps to maintain optimal operating pressure in the cooling system.

Because as the coolant heats up and cool down, the pressure goes up and down accordingly too. Too high of a pressure can crack the hoses while too low of a pressure will create air pockets within the system.

Pressure cap does that through the use of spring loaded valves.

  • When pressure exceeds a certain threshold, the spring loaded valve opens up and allows some of the coolant to flow into the reserve tank (a.k.a overflow tank). This relieves the pressure from the cooling system.
  • When pressure drops below a certain threshold, the valve we talked about above closes. Instead, it opens up another set of valve which pulls coolant from the overflow tank and into the system.

Component #5: Water Pump

The picture showcases what is inside a water pump. You can see a large metal blade on the right that is used to generate the pressure.
This is what you would see inside of the water pump!


Original image by Razor512 (CC BY 2.0), edited by D S Auto.


The coolant don’t have enough energy to flow by itself.

That is where water pump comes in.

It is a vane-type pump that is driven by the engine belt. It increases the pressure of the coolant so that they have enough energy to circulate around the car cooling system.

Component #6: Thermostat

Thermostat has a wax-like substances that melts during high heat, which prevents the coolant from circulating to the radiator.
Thermostat has a wax-like substances that melts during high heat, which prevents the coolant from circulating to the radiator.


Image by Hoikka1 (CC BY-SA 3.0).


Thermostat is a small component (about 5 cm in diameter) that controls the flow of coolant throughout the system. Very similar to a pressure cap.

But, instead of regulating the pressure, it regulates the temperature.

Our car engine needs to operate between 90 and 110 degree Celcius for best performance.

When the engine is below 90 degree Celcius, thermostat blocks the flow of coolant so the engine can heat up to the operating temperature quicker. Vice Versa.

Component #7: Hoses

Hoses are rubber pipes which connect the various components of the cooling system. They are designed to easily withstand the pressure inside the cooling system. Hey need to be replaced if you see any wear and tear, or they look dry, cracked too soft and spongy.

How engine cooling system works?

Check out this amazing animation on How Car Cooling System Works by Automotive Basics.

The seven components above come together like a well orchestrated symphony to cool our engine.

Here’s how it works.

  • Inside the engine, petrol are ignited to move the pistons. Heat are produced as a by-product.
  • When that happens, coolant flows through the radiator pipes. They are in close proximity with the hot engine pistons.
  • The heat gets transferred into the coolant and it becomes hot.
  • The heated coolant then flows through a hose and arrives at the radiator, which is always found at the front of the car (inside your car’s bonnet and next to your car headlights).
  • The hot liquid enters the radiator.
  • At the same time, our car is moving forward, which meets incoming air through the car grill and then the radiator.
  • A radiator fan is located nearby to increase the airflow and force them towards the radiator.
  • The colder incoming airflow then meets the hot coolant, which helps to cool it down.
  • Also, because radiator are compact windings of aluminum tubes and have such large surface area, the heat transfer becomes so much more effective.
  • By the time the coolant reaches the bottom of the radiator, it is sufficiently cooled.
  • It then returns back to the engine to absorb more heat.
  • The cycle repeats itself!


As we’ve mentioned, the engine needs to operate between 90 to 110 degrees Celcius. It should not be too hot or too cold.

If too much coolant flows through the engine, it may absorb so much heat that it starts to decrease engine performance.

That’s why, we have a thermostat to regulate the flow of coolant.

Here’s how it works.

  • Thermostat are found between the engine and the radiator.
  • If the coolant temperature is below the preset temperature, the thermostat blocks the coolant from flowing back into the radiator. Hence, the coolant circulate in the engine through a bypass route until it heats up sufficiently.
  • Once it exceeds the temperature, thermostat opens up so that coolant can flow back to the radiator to be cooled down.
  • This maintains optimal operating temperature in the engine compartment.

Well there you have it, that is how your car engine cooling system works.

Signs of a bad cooling system

Having understood what our engine cooling system works, I’m sure you see why it’s important to maintain a functional cooling system.

Unless you and your friends love pushing cars for a good evening workout, I recommend that you always keep it in tip-top condition.

Watch out for these symptoms of a bad cooling system.

Problem #1: Leaking coolant

This is one of the easiest problem to spot. All you need is just a pair of good eyes, and know where to look.

Here are some symptoms that you can notice.

  • If you find liquid dripping underneath your parked car, it may be a sign of a leaking radiator.
  • When your low coolant light comes on, you most probably have a leaking radiator.
  • If you have to constantly refill your coolant tank, you definitely have a leaking radiator.

Now that you know you have a leaking coolant, don’t just keep refilling your coolant, take your vehicle to get it properly diagnosed and repaired.

It will pay off in the long run.

Problem #2: Vehicle overheats

If you notice water vapour coming out from your car’s bonnet, chances are you have a faulty car cooling system. You can’t miss it, it’ll look like white smoke.

As soon as you see the water vapour, stop your car in a safe place and let the car cool for at least half an hour. It’s important to do that to avoid burning yourself.

When the car is cooled enough, open up the car’s bonnet and check your coolant level. A low coolant level could very likely be the culprit. You may add some water if it’s below the minimum coolant level. Yes, it will dilute the coolant but it’s better than nothing at this point!

Once you get your car up and running, definitely get it inspected by a local mechanic as soon as you can to avoid being stuck with an overheated car again.

Problem #3: Sludge in the radiator

Over time, the walls and tubing of our car cooling system can rusts. When the coolant circulate around the system, it accumulate these tiny particles and deposits.

You will start to notice two things.

  • The coolant have turned into brownish color.
  • It starts to flow less freely, like a sludge or a gel.

These are clear signs that you need to flush your car coolant. Otherwise, it will hinders the proper functioning of the radiator.

If left unattended, it can cause damage to your engine cooling system, which is very costly to replace.

Problem #4: Bad Water Pump

A worn water pump will usually manifests itself in a low-pitch whining noise, coming from the front of the car.

To check, simply start your car engine with the bonnet up. Listen very carefully for the source of the sound. If the noise is coming from the water pump, you know you need to get it replaced.

However, it is worth pointing out that a worn power steering pump, alternator, and AC compressor will also exhibit similar sound. So, make sure you pay full attention when you are trying to pinpoint the source of the noise. Otherwise, you may end up replacing a part that you don’t need.

If you notice any of the above symptoms, you know it’s time to pay your local workshop a visit.

The Bottom Line

That’s it!

That is exactly what a car cooling system is, and how it works.

Have you car ever overheated? Is it because of a bad car cooling system?

Leave a comment down below if you have. We would love to hear about your experiences.

Until then, drive safe and drive smart!

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