What is Engine Cooling System?- Types, and How it Works

When you’re out on the road, your vehicle generates a lot of heat. That heat and friction is concentrated in the engine, which requires your car’s cooling system to be working effectively to prevent overheating.

Your vehicle’s cooling system is comprised of many different parts, including the radiator, radiator fan, hoses, thermostat, and water pump. Given how hard these components are working regularly, it makes sense that over time they might wear out and need to be repaired or replaced.

Becoming familiar with how the cooling system works and some common signs of issues can help make you more aware of possible repairs. Keep reading to familiarize yourself with this important vehicle system!

What is a cooling system?

A vehicle’s engine-cooling system not only keeps the engine cool but keeps its temperature warm enough to ensure efficient, clean operation.

System components include a radiator to remove heat, a fan or fans to ensure adequate airflow for radiator cooling, and a thermostat valve that opens when the desired operating temperature is reached and circulates coolant through the engine.

To do this a water pump (or coolant pump) is included. and other components. Most vehicles now use an expansion tank that allows coolant to expand and exit the cooling circuit when it is hot, and when the car is stopped and the engine is cold.

The cooling system also includes elements of the cabin ventilation system, as engine heat is used to heat the car interior.

How Does An Engine Cooling System Work?

In order for an engine to stay cool, engine coolant (also known as antifreeze for its ability to withstand freezing) is circulated through passages inside the engine block where it absorbs heat by way of conduction.

The warmed coolant then leaves the engine and carries the heat with it, allowing the engine to cool. For this cooling process to happen, several components need to function properly. The radiator, coolant hoses, water pump, thermostat, expansion tank, and heater core are all integral parts of the engine cooling system.

Once the coolant draws heat out of the engine, it passes through an upper coolant hose (or “radiator hose”) on its way to the radiator. The radiator is a series of narrow pipes through which the heated coolant passes.

These pipes are woven through a matrix of wafer-thin aluminum ribbons (or “fins”) that absorb the heat through the pipes, from the coolant. Air passing through the radiator draws the heat away by means of convection. The cooling fan helps to move a higher volume of air through the radiator. The coolant temperature drops and the coolant cycles back to the engine through the lower hose.

The water pump is the component that forces the coolant through the system. If the water pump is not working properly, the coolant will not flow and the engine will overheat. The water pump is driven by either the serpentine drive belt, or by the engine timing belt.

If coolant is allowed to circulate constantly, the engine will be unable to reach a high enough temperature to work properly. So the coolant flow must be controlled. The thermostat is a valve that is tasked with regulating the flow of coolant.

It remains closed until the engine reaches its maximum operating temperature. Then the thermostat opens to allow circulation until the engine drops to to its minimum operating temperature. A faulty thermostat is a common cause of overheating problems.

A couple other components are also at play in the cooling system. The coolant expansion tank, sometimes referred to as the overflow bottle, keeps the car from losing coolant when its temperature rises over its boiling point.

The heater core is not directly part of it but is attached to the cooling system. Some of the heated coolant is diverted to the heater core (something like a small radiator) located beneath the dashboard. A fan blows through the heater core and transfers heat to the passenger compartment to warm the occupants on cool days.

the Parts of the Engine Cooling System

The major components of the cooling system are the water pump, freeze plugs, thermostat, radiator, cooling fans, heater core, pressure cap, overflow tank, and hoses.

Parts of engine Cooling system

1. Cooling Fan

The cooling fan is located at the very front of the vehicle and is designed to turn on when the coolant (we’ll talk more about this in a minute) begins to get too hot. It will turn back off once the coolant has lowered in temperature.

2. Radiator

The radiator is specially designed in order to remove the heat from the coolant by transferring it to the air blown through the radiator by the fan and incoming air from driving. Radiators are prone to leaking after years of use.

3. Water Pump

The water pump is what propels the coolant through the engine. A broken water pump will prevent your cooling system from operating, thus resulting in the engine overheating while driving.

4. Thermostat

The thermostat is what controls the operation of the cooling system, specifically turning the fan on and off.

5. Hoses

A series of rubber hoses connect the radiator to the engine in which the coolant flows through. These hoses can also begin to leak after many years of use.

6. Antifreeze/Coolant

The bread and butter of the cooling system is the coolant. This sweet-smelling, bright green fluid flows through passages in the engine, attracting heat from the engine. It collects the heat and transfers it to outside air inside the radiator.

Types of Engine Cooling Systems

Generally, there are two types of cooling systems, and those are:

  • Air-Cooled Engine
  • Liquid-Cooled Engine

#1. Air-Cooled Engine.

An air-cooled engine uses air circulation to dissipate heat from the combustion process. It features cooling fins on its cylinders and the piston cylinder head’s top to increase the surface area that radiates heat.

The cooling fins pull heat from the cylinders and release thermal energy from the engine. They make it possible for the latter to stay at safe operating temperatures.

While cooling fins improve passive heat dissipation, air-cooled engines, such as in motorcycles, receive a lot of airflow while the motorbike is traveling. Air rushes through the exposed cooling fins, especially at higher speeds.

In other vehicles with air-cooled engines, a cooling fan pushes air through metal shrouds surrounding the fins because, unlike in a motorcycle, airflow from simply moving forward isn’t sufficient. In older vehicles, the fan draws power from the engine via a connective belt. Newer fans have an electric motor that runs on the vehicle’s power supply.

#2. Liquid-Cooled Engine

As its name indicates, the liquid-cooled engine uses liquid coolant to regulate its temperature. Some call it the water-cooled engine, but its cooling system doesn’t use pure water. Instead, the coolant is a mixture of water and antifreeze.

The liquid-cooled engine employs a closed-loop cooling system that runs efficiently even when the car isn’t moving. The system includes various parts that work together to keep the engine running within a safe temperature range.

A water pump moves coolant through the engine and cooling system. However, when the engine is cold, the coolant will bypass the thermostat to be directed through the heater core, providing cabin heat in wintertime.

Cabin heat on air-cooled engines is typically accomplished using shrouded fins on some of the exhaust parts, with the cooling fan forcing air across the fins and into the vehicle when the heater controls are open.

Liquid-cooled engines have a radiator. This heat exchanger usually features cooling fins similar to those on the cylinders of an air-cooled engine. The radiator removes heat from the coolant passing through its tubes and dissipates the thermal energy through its fins.

Radiators have a fan that forces air over their cooling fins. There are airflow dynamics involved, so the fan either doesn’t pull as much air or doesn’t work at all while the vehicle is traveling above certain speeds.

A thermostat controls the movement of coolant to and from the radiator. The thermostat ensures that cooling fluid enters the radiator at the right time and temperature and helps the liquid-cooled engine warm up more quickly.

Each of these parts plays a vital role in a water-cooled engine. The water pump moves coolant through the system, where the fluid can absorb the heat produced by the combustion process.

The thermostat monitors the coolant’s temperature. It prevents any flow to the radiator until the coolant gets hot enough. Then it opens the appropriate valve and lets hot liquid enter the radiator to cool off. This way, it keeps the engine coolant at a constant temperature, not too hot or cold.

The Most Common Car Cooling System Problems

Even when you keep up with maintenance and check your car’s cooling system often, things can still become damaged or worn out. If you’re wondering how to tell if your radiator is bad, check for these symptoms:

  • Your vehicle is running hot or is overheating.
  • A fluctuating temperature gauge.
  • Steam coming from under the hood.
  • White exhaust fumes
  • Low coolant levels
  • Coolant is leaking under vehicles.
  • Decreased/poor gas mileage.

If you think something might be wrong with your radiator or cooling system, getting it checked by a professional is important. A trained automotive technician will be able to diagnose the cause of your problem. Here are some of the most common issues:

Radiator Leaks

Leaks can spring up from a few locations in your radiator, including the hoses. Some radiator leak symptoms include puddles of coolant underneath your vehicle or low coolant levels. You might even notice white exhaust smoke, which can indicate burning coolant due to a leak.

Air in the Cooling System

If air gets into the cooling system, it can reduce the system’s ability to maintain the proper temperature and regulate your engine’s performance. Air in cooling system symptoms commonly include rises or frequent fluctuations in temperature. Air in the cooling system is considered to be one of the top causes of engine overheating.

Thermostat Issues

Problems with the car thermostat are generally easy to notice. The gauge reading high or changing erratically are some of the more common signs. You also might notice coolant leaks around the thermostat housing.

Water Pump Failure

Rust can start to build up on a water pump and cause corrosion of the metal, which can create small holes on the pump’s surface. High-pitched sounds coming from the front of the motor might indicate a loose water pump pulley. Coolant leaks can also be a symptom of a failing water pump.

Low Coolant

Low coolant can be one of the main causes of issues with the cooling system. Low coolant signs can include a dashboard warning light on some vehicles, rising temperature gauge or the internal heating system having issues working.

What Goes into Car Coolant?

If car coolant was just plain water, life would be a lot simpler but water contains impurities that corrode the cooling system and reduce its efficiency. Not only that but water also boils at 100C and freezes at 0C.

This last characteristic is a bad as having no coolant at all since, being frozen, the coolant will not flow and the water pump will not rotate, which means the engine will get hotter and hotter until it seizes. If the water pump is driven by the timing belt, the seized pump could damage the belt. Frozen coolant expands, too, causing serious damage to the engine block and pipes.

Instead, car coolant is a mixture of water and antifreeze. Most manufacturers now recommend using de-ionized water (in other words all the minerals such as sodium and calcium have been removed). The anti-freeze contains additives including corrosion inhibitors.

Coolant can be made by mixing de-ionized water with anti-freeze concentrate, or it can be bought pre-mixed, ready to be added to the cooling system. If you’re mixing your own coolant, stick to a ratio of 50/50 anti-freeze and water. Any less or more will reduce the effectiveness of the coolant.

At this point, it’s important to know that anti-freeze is quite an aggressive chemical and that it’s important you use the right type of anti-freeze in your car, especially since it’s possible to buy it separately from coolant and add it as necessary. Don’t leave anti-freeze puddles on the ground – it’s poisonous!

Most cars made since 1998 have aluminum engines and radiators for which only organic acid technology-based (OAT) anti-freeze is suitable. Cars built before 1998 can use its non-organic acid technology alternative. There are two other types in common use, too; one that’s based on ethylene glycol and another on propylene glycol.

Anti-freeze comes in different colors according to the cooling systems it’s compatible with and it’s best to top-up, if you have to, with the same one.


What Is the Cooling System?

The cooling system serves three important functions. First, it removes excess heat from the engine; second, it maintains the engine operating temperature where it works most efficiently; and finally, it brings the engine up to the right operating temperature as quickly as possible.

How Do I Know If My Cooling System Is Bad?

Six Signs of Cooling System Problems:
1. Low Fluid Level.
2. Poor Quality Coolant.
3. Coolant Leak.
4. Engine Overheating.
5. Engine Not Starting.
6. Warning Lights.

What is the most common cooling system problem?

One of the most common yet serious problems that develop in the cooling system is a radiator leak. A crack or leak from the radiator can lead to significant loss of coolant or antifreeze. Without these fluids present in the cooling system, air bubbles start to develop.

How much does it cost to replace coolant system?

The cost of a coolant or antifreeze change will depend on the type and size of your vehicle. On average you can expect to pay between $100 and $200 for a standard coolant change.

How does the cooling system cool down the engine?

For an engine to stay cool, engine coolant (also known as antifreeze for its ability to withstand freezing) is circulated through passages inside the engine block where it absorbs heat by way of conduction. The warmed coolant then leaves the engine and carries the heat with it, allowing the engine to cool.