Most modern internal combustion engines are generally cooled by liquid coolant through channels located inside the engine blocks & the cylinder head. The coolant does the job of absorbing the heat & then it releases the same inside a heat exchanger or radiator. Though they are ultimately cooled by air, but they are actually known as water – cooled because of the presence of the liquid coolant. On the contrary, the heat generated in an air – cooled engine is directly released into air (Direct Cooled Engines). Generally, this is favoured with the use of metal fins which cover the outer part of the cylinder head & the cylinders which help increase the surface area for the air to act upon. Air sometimes can be force fed with the help of a fan & shroud to get a better cooling with large volumes of air or only natural air with the help of well designed and well shaped/ angled fins. There are combustion engine which make use of exhaust pipes to release most of their heat and not air – cooled engines and liquid coolant. Some is lost through oil, some through lubrication & some through a cooler.
These air cooled engines have great application in 2 wheelers & was of great use during the mid twentieth century. Some Diesel engines still make use of this air – cooled engine. Most aviation engines are air – cooled whereas some use a combination of air – cooled and liquid cooled.