Air cooled

Most modern internal combustion motorcycle engines are cooled by a closed coolant system carrying engine coolant through channels in the engine block. The coolant, which itself is designed to pick up and lose heat quickly, absorbs the intense temperatures in the engine and passes to the radiator where it releases the heat to the passing air (hence why the radiator is at the front of the motorcycle, directly in contact with the air funneled in above the front wheel.

However, as this system uses a water based coolant, it is labelled a 'water cooled' engine.

An 'air cooled' engine is simply where the heat generated by the engine is released by a series of metal fins convering the cylinders of the engine itself. The fins increase the surface area that the 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.