About the coolant system and its role.

At best only 30% of the energy from consumed fuel goes to driving the car. The rest is released as heat. The engine is working best at a certain temperature. When this temperature is reached the heat produced must must somehow be brought away from the engine and its environment.

The coolant system let the engine heat up to that temperature and thereafter it takes away all the produced heat not necessary to hold the engine at the right temperature. Some of the excessive heat can then be used to heat the cabin and the rest is spilled out.


Water based coolant systems

Water is pumped through the whole coolant system in a circular manner. It has a pump that drives the water flow. The water from the pump typically is driven right into the motor. The coolant system have channels inside the motor through which water flows. It also has a heat exchanger, called radiator, through which water from the motor passes. The heat is delivered to air passing through the radiator. A fan blows air from the outside through the radiator.

At the place where the fluid leaves the motor, it also goes through the thermostat. This device measures the tempersature in the water, and it can send the water in two directions, either through the radiator or in a tube back to the pump. By sending the right amount of water in the two driections it can regulate the coolant effect and thereby the temperature of the engine.

The water pump is a cetrifugal pump driven by a belt connected to the crankshaft of the engine. The water goes into the pump near the center and is pushed by a fan inside the pump to the periphery inside the pump and out again to a tube leading into a channel system in the engine.

One important part of the system is the system of channels through the engine. The water from the pump is driven through these channels. When it enters the channels, the temperature is fairly low. In its way through the channels the water takes up heat from the engine and cools it. The water leaving the motor has the temperature of the metallic block of the engine. Usually the water first goes through channals around the cylinders and then through channals in the cylinder head.

The radiator consists of a system of many thin tubes or channels spaced apart so that air can flow between the tubes. The air between the tubes takes up the heat so that the water leaving the radiator is well cooled down.

At one of the sides of the radiator there is a fan. The fan can be electrically driven or driven by the belt coupled to the crankshaft. The fan blows the cooling air through the radiator.

There is another system taking heat from the engine, that is the cabin heater system. Some fluid from the cylinder head goes into the heater system. The heater consists of a radiator with an electric fan. The fan blows air through this radiator into the cabin where it is distributed by means of a system of channels. The fluid then goes back to the pump.


About air-cooled engines

In the 50-eths nd 69-eths air-cooled aniges were commonly produced, among which where the WW Beetles, the most widely produced cars ever.

Air cooling is in many ways simpler than water cooling. The air circulates around the motor parts and there are ribs and fins that bring the heat out to come in contact with the air and that direct the air along all parts of the mashinery. A fan in front of the motor blows air in the right direction towards the mashinery. In order to keep the cooling at the right level, the speed of the fan must be regulated by the thermostat. This is most easily done if the fan is driven electrically.

Air-cooling is also in some ways more reliant than water-cooling, since the system is not susceptible for breakage or leakage in the tubes and channals an have fewer mechanical parts. It is also as efficient as water-cooling.

However the effect of air-cooling is more difficult to controle. The speed of the air through the motor-room is also determined by the speed of the car and it is difficult for the fan to ajust to all swings in air flow rate occuring because of car speed and external conditions. Therefore it is difficult to constantly hold air-cooled engines at an optimal temperature.

It is difficult to regain the heat after the air has passed the engine parts to be used for heating the cabin. Also one looses the reservoir for heat in the cooling water that holds the motor room warm a long time after that the motor has been shut down, which is valuable in the winter season.

Air-cooling also makes much more noise by the air streaming along and aginst all kinds of constructions.

In an air-cooled car, the techical components in the moror room must also have more space between them, making it difficult to construct a compact motor room.

Because of these problems, air-cooling is not much used in car construction anymore, but are still much used for motorcycles and for aircraft engines.