Cooling system Part 2

There are several components in the cooling system and they all have important job.

The water pump circulates the coolant around the engine. It works in small and in the large circle the same. It is driven by a V-belt or a timing belt. Without it the coolant would still circulate but not as quickly and then the liquid would heat up to higher temperature and overheating of the engine could occur.

Modern radiators are made from aluminium. Coolant enters at the top right after it comes out of the engine and then travels though thin pipes to the bottom (or from side to side, then it is called cross-flow). All the way through it is cooled down. The heat is transferred from coolant to the pipes, from pipes to the aluminium fins and then it is radiated to the air. At the end of this process the coolant is ready to enter the engine all over again.

The fan takes care of air exchange in the radiator. It is equipped with shrouds which make sure new air is sucked in and the fan doesn't only circulate the same air. Earlier fans were drive by the V-belt, that's why they are still sometime called fan belts. But now it's usually electronically operated which has advantage over belt driven fan - it works only when it needs to and it doesn't use engine power to do so. When a vehicle flies through a motorway, new air doesn't need any help to get in. But if the car is stuck in the heavy traffic or just going slowly through a city on warm day, the air may need some help and in that moment fan gets in charge.

As one of the cooling system's job is to heat up the engine after start as soon as possible, a thermostat is used for this reason. It is valve which opens at predetermined temperature. Until then it stays closed, preventing the coolant to go the radiator. The coolant keeps circulate around the engine (what I call small circle) and warms up much faster. When that happens, the wax inside the thermostat starts to melt, valve opens and let the coolant to get through to the radiator and starting the large circle. In other words the operation depends on changes in volume of the wax around the melting point, the pressure becomes so great that it forces against a spring inside. When it is time for thermostat to close again, the spring returns the valve on its original place and closes the passage.

Cooling system Part 1

When I started with the cooling system, I had no idea how important it really was. But the temperature of the engine must be controlled all the time. If it isn’t then the combustion chamber walls, piston crown, upper part of the cylinder, valves can expand and change shape. Detonation (mixture of fuel and air starts to burn in more places at once) or preignition (the mixture self-ignites before the spark plug can create a spark) can occur. However, over cooled engine can cause many problems as well. It can reduce vaporising of the fuel in compression stroke and creates deposits on cylinder walls which will dilute the oil and destroy its lubricating properties. Or water vapour formed during combustion will form sludge with the oil and then corrode the engine parts.

Nowadays is used water-cooling instead of the air-cooling because it is much easier to control the temperature. But the engine operating temperature is around 90°C which is quite close to the boiling temperature. To prevent water from boiling, ethylene glycol is added which increases the boiling temperature and lowers the freezing temperature as well. But that is not all, when the car is running the coolant is kept under pressure and for every 4kN/m2 the boiling temperature is raised by 1°C. Another thing that is necessary to put into the coolant, before it is used in car, are rust, corrosion and foaming inhibitors. Because as we all know metal and water on its own is not an ideal combination.

The coolant is circulating around engine all the time, either in small or large circle (that is what I call it and will explain later). If it wasn’t, localised overheating would become a serious problem.

Recently I discovered that the warning on the cap of the reservoir is not only about our safety. You should never open the cap when the engine is still hot. That is not only because the coolant can come out and cause serious damage to you or somebody around you but also because the moment the cap is opened the system lose its pressurised state. It will try to equalise to the atmospheric pressure everywhere around and it can start to boil immediately which will destroy the hoses in the system.

The cooling system itself has more than only one job:

- it needs to heat up the engine and bring it to the operating temperature as soon as possible

- it needs to maintain the temperature at all costs

- and then it has to remove surplus heat from the engine