"Important: do not boil!"
In general, motorcycle (or scooter) engines are high performance machines which rev much faster than those of cars.
As the coolant ensures better engine temperature stability (therefore keeps performance constant, with less polluting emissions, due to lower energy losses), engines simply cooled by air are gradually tending to disappear.
Changing the coolant
The coolant needs to be changed as it can pick up particles due to corrosion in the engine and in time its characteristics and fluidity may alter, being a mixture of distilled water and glycol ethylene.
Its anti-freeze capacity is also reduced. It is commonly acknowledged that the optimum lifespan of a coolant is two years, after which there is a danger of the formation of scale which greatly reduces the overall efficiency of the system.