An air-cooled engine uses cooling fins cast into its cylinder head to dissipate heat instead of using a liquid-filled radiator. By eliminating the radiator, an air-cooled engine is able to be used in applications in which space restraints prohibit installing a radiator. As the air-cooled engine builds heat, the cooling fins allow the wind and air to move the heat away from the engine much like a person blowing on a piece of food that is too hot to eat. Used in every type of vehicle from aircraft, tractors and sports cars to motorcycles and boats, the air-cooled engine has proven reliable as well as durable. In applications such as aircraft use, the air-cooled engine prevents the extreme cold found in high altitudes from causing freezing problems such as those that plague liquid-cooled aircraft engines.
Popular in motorcycles due to its reduced weight, the air-cooled engine is used on some of the most expensive motorcycles as well as the most affordable models. Though often criticized for the tremendous amount of heat passed along to the riders' legs when sitting still, an air-cooled engine still remains the popular choice for many custom-built motorcycles worldwide. Many manufacturers of touring style motorcycles have elected to supply liquid-cooled versions in top-end motorcycles. The American-based Harley-Davidson motorcycle company, however, continues to offer air-cooled engine configurations as the primary engine package.
Many pieces of equipment used in the construction trade use an air-cooled engine to provide the power. This enables the equipment to be operated in severe climates without fear of freezing or overheating. By eliminating the radiator, water pump and coolant, there is far less maintenance required to keep the equipment up and running. Most non-liquid cooled engines operate at reduced engine speed, which reduces some of the wear and tear of the engine's internal components as well. One of the most notable exceptions to this rule is the chainsaw, which operates at a very high rate of speed.
Air-cooled engines that operate at high engine speeds are often 2-stroke versions. This type of engine uses a gas and oil mixture in the fuel tank, and the oil helps to cool the engine. This type of configuration also eliminates a great amount of oil in the engine's crankcase. The oil retains engine heat and adds to the cooling difficulties in a 4-stroke engine. This is why many 4-stroke engines require an external engine oil cooler to aid in maintaining proper temperatures.