rely on the circulation of air directly over hot parts of the engine
to cool them.
Most modern internal combustion engines
are cooled by a closed circuit carrying liquid coolant
through channels in the engine block, where the coolant absorbs heat, to a heat exchanger
where the coolant releases heat into the air. Thus, while they are ultimately
cooled by air, because of the liquid-coolant circuit they are known as water-cooled
. In contrast, heat generated by an air-cooled engine is released directly into the air. Typically this is facilitated with metal fins
covering the outside of the cylinder
which increase the surface area that air can act on.
In all combustion engines, a great percentage of the heat generated (around 44%) escapes through the exhaust, not through either a liquid cooling system nor through the metal fins of an air-cooled engine (12%). About 8% of the heat energy finds its way into the oil
, which although primarily meant for lubrication
, also plays a role in heat dissipation via a cooler
use air cooling for the sake of reducing weight and complexity. Few current production automobiles have air-cooled engines (such as Tatra 815
), but historically it was common for many high-volume vehicles. Examples of past air-cooled road vehicles, in roughly chronological order, include:
- Franklin (1902-1934)
- GM "copper-cooled" models of Chevrolet, Olds, and Oakland......