All vehicle engines are air-cooled to some degree. Even in water-cooled engines heat is transmitted first from cylinder to water and afterwards, in the radiator, from water to air. This method of cooling is not difficult to accomplish, because the heat taken off the hot cylinder walls by water can be distributed without difficulty upon the large cooling surface of the radiator, and so easy transmission of air is made possible.
Reciprocating engines used in aircraft are almost entirely air-cooled. Aircaft engines cooled by air are manufactured today in sizes ranging from 50 to 3500 hp and they superseded water-cooled engines. The principal advantages of air-cooled aircraft engines are low weight, and greater reliadilim reliability in operation. Modern motor-cycles are also designed almost exclusively with air-cooled engines.
New designs of air-cooled vehicle engines are notable for their easy maintenance, reliability and economical operation.