Engine cooling: functioning and components
The cooling system of a car is more complex and useful than you can imagine. In addition to cooling the engine block, which is heated by combustion, it also serves other organs. Moreover, the engine temperature is a determining variable for pollutant emissions, so the brands have developed very technical circuits that are closely monitored by electronics.
Let's take a look at the main features of the system used to cool the engine and some of its auxiliaries.
Components of the circuit
Before looking in more detail at the functioning of the cooling system, let's have a look at the components that make it up (if you want to skip this part, go a little further down).
Liquid
If you can put water in the circuit it is not recommended. In case of freezing, the expansion will break some organs and hoses that have ice in them.
Moreover, you should not put coolant randomly, you must respect the manufacturer's recommendations because some elements of the circuit may corrode ...
Water pump
As you may have guessed, the water pump is used to circulate the water in the circuit. Note that there was a time when it was not necessary to have a water pump, the simple temperature differential (which induces a depression a bit like the voltage with the + and - poles) between hot and cold water was enough to circulate water.
The water pump is either driven by the engine (its speed depends on the rpm) or it is electric (top diagram) for the most modern ones where the computer controls the engine temperature to the nearest degree. It is also common to have several water pumps on the circuit.
Water box
This organ acts as a router for the water, i.e. it directs the liquid to several areas where there are organs that need it, so I think of the exchangers.
Fan
In case of excessive heating in the water circuit, and if the car does not move fast enough to bring air to the radiator, the fan can take over (with two possible rotation speeds). The fan can also be used to cool the air conditioning condenser.
Thermostat
is used to "enlarge" the water circuit when the engine reaches temperature. In fact, in order to increase the heating speed, the water first circulates in a smaller circuit that is not connected to the radiator. Once the engine is warm, the thermostat opens and allows the water to circulate in the larger circuit where the air cooler is located. See the diagrams below to understand. This thermostat can be electric or mechanical (it contains a wax that becomes liquid when heated: this allows the small valve to open by a clever mechanism).
Expansion tank
serves both to supply the system with water if it should run out and to act as an expansion tank to release excess water into the system. Sometimes the pressure can cause leaks when the cap does not hold the pressure very well. Modern cars often have a device that prevents the vessel from being opened when the water is hot, to avoid splashing that could lead to burns.
Heat exchangers
Various and varied, the exchangers often use the engine water to cool the air (water/air exchanger) or oil (water/oil exchanger). This makes it possible to cool the oil or the air in order to make it denser (and thus to make it enter more into the engine. The exhaust gases passing through the EGR valve are also cooled by an exchanger.
Why not put normal water in the circuit?
Why is it not advisable to use tap water in the cooling system?
Well, you should know that the products specially designed for engine cooling have very useful properties for this mission. On the one hand, if it freezes it will not freeze (solidify) below -20° while water freezes at 0° (but you should already know that!). It can be dangerous for the engine to operate with a circuit filled with ice (and not with liquid water) for circulation reasons. Imagine how the water pump would react if it is stuck in the ice... Finally, it is important to know that water in a solid state takes up a larger volume, so ice takes up more space than liquid water, which can cause some of the hoses in the cooling system to break and therefore cause a leak...
Finally, specialized products have properties that improve their ability to cool.