A Short Course on Cooling Systems

A Short Course on Cooling Systems

A modern car consists of a large number of parts, components, mechanisms, and systems. All systems are crucial, and it would be foolish to argue about which of these systems is more important and necessary.

Now we will consider one of such systems without which operation of the engine would be impossible - a cooling system.

Why does a car need a cooling system? The cooling system serves to maintain normal thermal conditions of the engine and remove excess heat, regardless of operating conditions. The temperature of gases in the cylinders of a running engine reaches 1800-2000 °C. Only part of the heat released during this (for carburetor engines - 21-28%) is converted into useful work. Part of the heat (12-27%) is removed with the coolant; otherwise, the engine parts overheat, and their wear increases sharply. Excessive increase in engine temperature also leads to burnout of the lubricant. A significant decrease in the temperature of a running engine is also undesirable. In a supercooled engine, power decreases due to heat loss. Friction losses increase due to thicker lubricant, part of the working mixture condenses, flushing the lubricant from the cylinder walls, and wear of parts increases. In a subcooled engine, corrosive wear of the cylinder walls increases as a result of the formation of sulfur and sulfur compounds.

From the above, it follows that the cooling system is very important and that without it, the car will not be able to drive even a short distance.

The cooling system, in addition to the primary function of engine cooling, performs several other functions, which include:

  • heating air in the heating, ventilation, and air conditioning system;
  • oil cooling in the lubrication system;
  • cooling the exhaust gases in the exhaust gas recirculation system;
  • cooling air in the turbocharging system;
  • cooling the working fluid in an automatic transmission;

In general, there are two types of cooling systems for internal combustion engines: air and liquid. Let's look at them in more detail.

Air cooling

Air cooling

Air cooling can be natural or forced. Natural air cooling is the simplest type of cooling. The heat from an engine with such a cooling system is transferred to the environment through the developed ribbing on the outer surface of the cylinders. The disadvantage of the system is that, due to the low heat capacity of the air, it does not allow evenly removing a large amount of heat from the engine and, accordingly, creating compact, powerful power plants. Natural air cooling is common on engines of light, highly mobile equipment: motorcycles, mopeds, aircraft, and car models. With the systematic increase in the forcing of motorcycle engines on the most advanced models, air cooling gives way to liquid cooling. Due to the low mass, natural air cooling was also widely used on piston aircraft engines, where the rotor blades close to cylindrical and having a low circumferential speed of the butt of the propeller blades practically did not work as a fan, but the speed of the incoming flow onto the aircraft was very high in itself.

Stationary or tightly bonded engines are equipped with a forced-air cooling system. In them, with the help of a fan, an airflow is created, which blows over the cooling fins. The fan and finned surfaces are usually covered with a guiding cover. The advantages of such an engine are similar to those of naturally cooled engines: simplicity of design, low weight, lack of coolant. However, such engines are distinguished by increased operating noise and large dimensions. In addition, when designing such engines, problems arise with the cooling of individual elements of the engine structure due to uneven airflow.

In passenger cars made in Europe, air cooling was widely used in the 1950s and 1970s. These are mainly small cars such as Volkswagen Kafer, Fiat 500, Citroën 2CV; the representative Tatra 613 stands apart. Trucks with air-cooled diesel engines were produced (for example, trucks under the Tatra brand from the beginning of production and until the beginning of 2010 were equipped exclusively with such engines). Air-cooled engines have many tractors that have steady engine operating conditions and specific requirements for ease of maintenance. Currently, forced air cooling is used on most scooters, motorized tools (chainsaws, lawnmowers, etc.), engines of small generator sets, walk-behind tractors, and other self-propelled and stationary small agricultural and communal machines. For the latter, unified rows of simple one-two-cylinder air-cooled engines are very common, the same for different manufacturers (Briggs & Strattonruen, Honda, Subaru, Chinese), in the form of a compact finished unit with a horizontal plane mount.

Liquid cooling

Liquid cooling

The liquid engine cooling system consists of several elements. The most difficult one is called “cooling jacket”. This system is a branched network of channels in the thickness of the cylinder block and cylinder head. In addition to the jacket, the system includes a radiator for the cooling system, an expansion tank, a water pump, a thermostat, a radiator fan, metal and rubber connecting pipes, sensors, and control devices.

The system is based on the principle of forced circulation, which is provided by a water pump. Due to the constant outflow of the heated fluid, the engine is cooled evenly; this explains the use of the system in the vast majority of modern cars.

Having passed through the channels in the walls of the block, the liquid heats up and enters the radiator, where it is cooled by the airflow. When the car is moving, natural airflow is sufficient for cooling. And when the car is at a standstill, airflow occurs due to an electric fan, activated by a signal from a temperature sensor.

Details on the key elements of water cooling

Cooling radiator

The radiator is a panel made of small diameter metal tubes covered with aluminum or copper "plumage" to increase the heat transfer area. In essence, the plumage is a repeatedly folded ribbon of metal. The thermostat area of ​​the tape is large enough, which means that the radiator can release a lot of heat into the atmosphere per unit of time.

The most vulnerable element of the engine design is the turbocharger (turbine), which operates at extremely high speeds. When overheated, destruction of the impeller and shaft bearings is almost inevitable.

Thus, the heated liquid inside the radiator circulates at once through the numerous thin tubes and is cooled quite intensively. A safety valve is provided in the radiator filler cap that removes vapors and excess liquid that expands when heated.

In the radiator of a car with an automatic transmission, a second, independent circuit is provided in which the transmission fluid is cooled.

Expansion tank

The expansion tank serves to compensate for the expansion of the liquid when the temperature rises. The reservoir can be "simple" or "complex", depending on the system design. A "simple" tank is a container for collecting excess liquid expanded from heating. A rubber tube is brought to it through the lid; the other end is connected to a branch pipe in the upper radiator tank.

In a more complex version, the tank is a full-fledged part of the cooling system. It is pressurized, and a diverting valve is installed in the tank lid. In this case, there must always be liquid in the reservoir so that air does not enter the radiator when the engine temperature drops. For control, the Min and Max marks are applied to the wall of the tank under pressure.

Water pump

The water pump circulates the coolant in the system. As a rule, it is a centrifugal pump in which pressure is created by an impeller with complex-shaped blades located inside the housing on the central axis.


The thermostat is a device that maintains a constant temperature in the cylinder block. It does not allow the liquid to overheat the engine. It regulates the volume of coolant that flows through the radiator.

Cooling fan

In some cases, the incoming airflow may not be enough to blow the radiator effectively. To ensure heat dissipation, a fan is provided in the car cooling system. In cars with rear-wheel drive and longitudinal engines, a mechanical fan is often used, which is driven by a belt from the front crankshaft pulley. The rotational speed of the blades is regulated by a thermal coupling (a type of viscous coupling) to which the impeller is screwed.

If you attach the fan impeller to the pulley without a thermal coupling, when the engine is spinning over 3000 revolutions, the impeller blades will break off.

Front-wheel drive (and most modern rear-wheel drive) vehicles use an electric fan. It is connected to a diffuser, which is screwed to fasteners located along the contour of the radiator. The advantage of the electric fan is the ability to flexibly control its operation using a controller, guided by the readings of the coolant temperature sensor.

Auxiliary elements

The liquid cooling system also includes typical control elements: an electronic unit, a temperature sensor, etc., as well as devices for draining the liquid. The fluid must be drained, for example, to repair the engine.

Diagram of the liquid cooling system

Diagram of the liquid cooling system

The circulation of the coolant in the system occurs in small and large circles.

The small circle is involved when starting a cold engine and provides it with a quick warm-up. Moving in a small circle, the liquid does not pass through the radiator.

When the coolant temperature rises to 80 degrees, the main thermostat valve opens slightly, and circulation continues in a large circle that includes the radiator. (The thermostat can also be graduated for a different opening temperature).

When it reaches a mark of 94 degrees, an additional thermostat valve begins to close, limiting the access of coolant to a small circle - from the engine to the pump. Thus, the thermostat does not allow overheated liquid to enter the walls of the cylinder block, preventing overheating.

Depending on the operating mode of the internal combustion engine, the cycle of movement of the coolant in the system may vary. The volume of fluid circulating in each circle directly depends on the degree to which the main and additional thermostat valves are open. This circuit provides automatic maintenance of the optimal temperature regime for the engine.

Pros and Cons of a Liquid Cooling System

Water pump

The main advantage of liquid cooling is that the engine is cooled more evenly than if the unit is blown with an air stream. This effect is due to the higher heat capacity of the coolant compared to air.

The liquid cooling system can significantly reduce the noise from the engine running due to the thicker block walls.

The inertia of the system does not allow the engine to cool down quickly after shutdown. The heated liquid is used to heat the vehicle interior and to preheat the combustible mixture.

Along with this, the liquid cooling system has several disadvantages.

The main disadvantage is the complexity of the system and the fact that it operates under pressure after the fluid has warmed up. A pressurized fluid places high demands on the tightness of all joints. The situation is complicated by the fact that the operation of the system implies a constant repetition of the heating-cooling cycle. It is harmful to joints and rubber tubes. When heated, the rubber expands and then contracts when it cools, causing leaks.

In addition, the complexity and a large number of elements in itself serve as a potential cause of "man-made disasters", accompanied by "boiling" of the engine in the event of failure of one of the key parts, for example, the thermostat.

What to fill in the engine cooling system?

First, let's remember what is in your cooling system? Not so long ago, it was quite common to find cars with water in the engine cooling system instead of antifreeze. Fortunately, the use of water as a coolant has become the exception to the rule these days. Usually, it is used in emergencies when something needs to be poured into the system, but there is no antifreeze at hand.

If we compare the characteristics of water and a special coolant (antifreeze), then the latter has many advantages. It has, for example, a higher boiling point, a low freezing point, and the presence of softening and anti-corrosion additives in the composition of softening and anti-corrosion additives that prevent the formation of scale and rust in the engine cooling system.

We have decided on this question - no water in the engine cooling system! But it should be borne in mind that the system’s durability largely depends on the quality of the coolant. You should not buy the first canister with the inscription "Antifreeze"; you should give preference only to products from reliable manufacturers with all the necessary certificates.

Most counterfeit fluids contain corrosive acids, which over time corrode not only the parts of the cooling system but also lead to the appearance of "cavities" even in the cylinder head! Therefore, we do not advise you to save on antifreeze.

Also, one of the important criteria for the quality of the coolant is the presence of special fluorescent additives in its composition, which help detect leaks in the engine cooling system. Since the system must be sealed, leaks in it are unacceptable.

Checking the cooling system for leaks

Checking the cooling system for leaks

Checking the engine cooling system for leaks is a very important stage in its maintenance. The fact is that in a sealed system, antifreeze boils at a temperature of 130 °C; under normal conditions, it boils at only 108 °C. Therefore, the slightest crack, for example, in the cooling radiator, rubber hose, or the expansion tank, breaks the tightness and the engine boils.

To facilitate the search for microcracks in the engine cooling system, special fluorescent additives, which are part of modern antifreezes, help - thanks to them, it glows in the rays of an ultraviolet lamp.

But, unfortunately, not every motorist has such a lamp. Therefore, in the process of maintaining the engine cooling system

m, we recommend adhering to a few simple rules:

  1. There are MIN and MAX marks on the expansion tank to check the fluid level. With a cold engine, the antifreeze level should be between these two marks.
  2. If the coolant level in the expansion tank is constantly decreasing, then this indicates a leak, that is, a violation of the tightness of the engine cooling system.
  3. Carefully inspect your radiator and pipes for leaks and smudges. If necessary, tighten the connecting clamps and make sure that the radiator cap is closed all the way.

The presence of air in the vehicle cooling system (the so-called "airlocks") can also disrupt its operation. Below, we will show you the easiest way to expel air from the engine cooling system.

The presence of air in the cooling system is checked as follows:

  • Open the cover of the expansion tank
  • Turn on the interior heating at full power and let the engine idle for two to three minutes
  • If there is air in the cooling system, bubbles will appear in the expansion tank

To remove air from the engine cooling system, the car must be placed at an incline so that the "front" is slightly "lifted" to the top. Further, the sequence of actions will be as follows:

  1. Open the radiator cap and start the car.
  2. Turn on the stove and let the engine run for a few minutes to allow air to escape from the system.
  3. After that, the motor can be turned off, and the radiator cap can be closed.

Now let's look at a few more nuances that you should pay attention to when servicing the engine cooling system to prevent the occurrence of malfunctions or to eliminate them.

What to look for when servicing the engine cooling system

To prevent malfunctions of the engine cooling system, it is necessary to regularly perform the following maintenance operations:

  • Checking the density of the coolant
  • Tensioning the drive belt
  • Cleaning the engine cooling system
  • Checking the thermostat
  • Checking the engine cooling fan

Checking the density of the coolant. The density of the antifreeze is checked with a hydrometer. At higher gravity, dilute your liquid with distilled water, and at a lower density, dilute with a similar coolant.

Tensioning the drive belt. One of the most common causes of overheating in a car engine (especially with a mechanically driven fan) is a loose drive belt. Belt slip reduces pump performance and, consequently, impeller speed.

Cleaning the engine cooling system. Also, do not forget to check the external condition of the motor and radiator. Both the radiator and the engine need to be cleaned regularly as dirt and debris interfere with the proper cooling of the engine. Often, the radiator is clogged with dirt, dust, poplar fluff, and other filth. All this debris can be easily removed with a strong jet of water or a powerful vacuum cleaner. Engine oil spills and dust adhering to them should also be washed off regularly.

Checking the thermostat. An important system engine is a thermostat, which ensures a high engine temperature and quick engine heating immediately after starting. How to check the correct functioning of the thermostat?

  1. Start the engine.
  2. Wait 2 minutes and go to open the hood.
  3. Now, probe the hose that leads from the radiator to the thermostat.
  4. After the engine has warmed up enough, a working thermostat will open a large circle and let the fluid through the radiator.

Checking the engine cooling fan. Another element that requires attention when caring for the engine cooling system is the fan. Most modern cars have electric cooling fans, controlled by a thermoelectric sensor screwed into the radiator. When the set temperature is reached, the sensor contacts are closed, and the fan starts to work, cooling the radiator surface. If the fan does not turn on when the engine heats up, then the reason for this may lie in the temperature sensor. The performance of the sensor is determined very simply. For this, you just need to close its contacts:

  • if the fan is running, then the sensor is faulty;
  • if not, the reason is either in the fan motor or in the electrical circuit of its power supply.

A Short Course on Cooling Systems FAQ

A Short Course on Cooling Systems FAQ
  • What is the normal temperature of antifreeze in a working engine?

The optimal temperature range with a warm engine (when the engine is fully at operating temperature) is between 80 and 90 degrees Celsius; this is the normal coolant temperature on a warm engine.

  • What would happen if I drove a car without a thermostat?

The main purpose of a car thermostat is to regulate the operating temperature of the engine. So, if you are driving without a thermostat, your engine will never reach its optimum operating temperature, and your heater may be blowing cold air.

  • Where can I buy cooling system parts?

You can find high-quality and inexpensive cooling system parts for any car on our Partsouq website.

  • What would happen if I poured water into the cooling system?

The engine will not react immediately to this; that is, it will start, it will work, and it may even be able to travel like that for some time. But in this case, both the cooling system and the power unit itself are at risk. Water will begin to boil already at 100 degrees, which threatens rupture of pipes, leaks, and breakdowns of the expansion tank. From contact with water, the metal parts of the cooling system will begin to rust, and a characteristic coating from the scale will also appear in it.