Engine cooling of internal combustion engines can be done according to several different principles. The division of the existing cooling methods is mainly based partly on which cooling medium is used in the engine itself, and partly on the manner in which the heat is transported away from the engine and the vehicle. Cooling is basically necessary due to the limited efficiency of engines, which means that not all heat energy produced is converted into mechanical energy. The excess heat must somehow be dissipated from the engine.
The coolant is usually either air or a liquid, which usually consists mainly of water with the addition of antifreeze (often glycol) and anti-corrosion agent. Modern car engines are almost exclusively liquid-cooled, while older cars such as the Citroën GSA and Volkswagen Type 1 are air-cooled. The last air-cooled passenger cars were made by Porsche and Tatra in the late 1990s.
Smaller internal combustion engines in mopeds, lawn mowers, etc. are usually cooled only with the help of cooling fins. For a car engine, it is required that the air is forced past the heat sinks by means of a fan. The air is a worse coolant than water, but on the other hand it is possible to supply large amounts of air from outside and blow out the hot air. The problem in cold climates is to recover heat to heat the passenger compartment, but there are technical solutions such as letting the ventilation air pass a heating chamber that sits around the exhaust pipes. Many cars with air-cooled engines also have a petrol-powered auxiliary heater. In cold weather, it also takes longer for an air-cooled engine to get warm, as you do not have a thermostat that turns off cooling. However, the cooling fan can be regulated by such. There is often an oil cooler that can help cool the engine.
The reason for choosing air cooling for a car engine was usually that it is cheaper to manufacture. The weight is also slightly lower, and you have no coolant that can boil or freeze. The disadvantages are increased fuel consumption due to more uneven temperature in the engine and in case of need for additional heat, as well as poorer heat in the car in winter. Exhaust gas purification is also usually more difficult to achieve. Since modern liquid-cooled engines often have a higher power in relation to their size, air-cooled engines have disappeared from cars more and more.
The fluid can in some cases self-circulate in the engine cooling system thanks to convection. It is more common, however, to have a pump that ensures that circulation in the system occurs and increases the efficiency of convection and heat transfer. The liquid used may be pure water, but for practical reasons a 50/50 mixture of water and glycol with additives is used to prevent corrosion.
Ultimately, all internal combustion engines in ground vehicles use ambient air as a secondary coolant, while boat engines can also use sea or sea water. What in principle distinguishes air- and liquid-cooled vehicle engines is whether a separate primary cooling medium is used or not. In liquid-cooled vehicle engines, there is usually a radiator where the heat is transferred from the primary coolant liquid to the secondary coolant air.
In addition to the usual cooling, there is often an oil cooler, which either conducts the heat into the ambient air or exchanges it for the coolant. In this way, the oil maintains a more comfortable temperature even under heavy load. Cars with automatic transmissions often have oil coolers for the automatic transmissions.
Principles for heat transport
The heat transport away from the engine and the vehicle takes place through some form of convection, which means that the heat is transported in an efficient way to the ambient air. Speed wind cooling means that the vehicle's own movement is used to achieve a convection. In fan cooling, a fan is used to force convection.