Liquid cooling (water-cooled engine)

A water-cooled or liquid-cooled engine has passages around the cylinders and head through which coolant, a mix of water and antifreeze, is pumped. The coolant carries heat to a radiator, where airflow, assisted by an electric fan at low speeds, cools it before it returns. A thermostat keeps the engine at its ideal temperature.

Compared with air cooling, liquid cooling keeps temperatures more stable, allows higher power output and tighter tolerances, and reduces mechanical noise. Today it is used on most motorcycles, from scooters and motocross bikes to tourers, not only high-performance models.

Maintenance: check the coolant level in the expansion tank, use the coolant type the manual specifies, replace it at the stated interval, keep the radiator fins clean and fit a radiator guard off-road. Overheating in slow traffic often points to a faulty fan or low coolant.