🌡️Cooling system

How it works

The cooling system keeps the engine within its ideal operating temperature range: an engine that runs too cold wears out faster and pollutes more, while one that runs too hot can seize and fail catastrophically. On a liquid-cooled motorcycle, a mix of demineralized water and antifreeze (glycol) with anti-corrosion additives circulates through channels machined around the cylinders and cylinder head, absorbs the heat, then releases it in the radiator, a network of fine channels and fins swept by airflow. Several components work together in this circuit. The water pump, driven by the engine, keeps the coolant moving. The thermostat, a heat-sensitive valve, stays closed while the engine is cold (so it warms up quickly) and opens at a set temperature (often around 80 to 85C, check your manual) to route coolant to the radiator. At a standstill or low speed, when airflow isn't enough, an electric fan triggered by a thermal switch takes over. The expansion tank absorbs the coolant's expansion when hot and allows you to top it up. The circuit is pressurized (the rated cap raises the boiling point). Failure modes include: low level (leak, missed maintenance), aged and corrosive coolant, a porous hose, a stuck thermostat, a dead fan or thermal switch, a clogged or punctured radiator, a worn water pump, or a head gasket. On an air-cooled motorcycle, there's no liquid or radiator: the cylinder fins, airflow, and oil (sometimes via an oil cooler) handle heat dissipation instead. Signs of a failing system: overheating, a temperature warning light, a fan that runs constantly, or a loss of power.

Maintenance tips

• ✓Check the coolant level regularly at the expansion tank (between Min and Max), always with the engine COLD. Never open a pressurized circuit while hot: you risk serious burns from the spray.
• ✓Fully replace the coolant at the recommended interval (often every two to four years, check your manual): its anti-corrosion additives wear out over time, and old coolant fosters scale buildup and corrosion in the circuit.
• ✓Use a coolant that's compatible with what's already in the system (ideally the same type/color), and never plain water alone (it freezes in winter, promotes corrosion, and has too low a boiling point).
• ✓Gently clean the front face of the radiator (bugs, mud) with a low-pressure hose from the inside out, and straighten bent fins with a proper fin comb - never use a high-pressure washer, which flattens them.
• ✓Periodically check the condition of the hoses (they should be supple, with no cracks or bulging) and that the clamps are tight: a porous hose or loose clamp causes a leak and overheating.
• ✓From time to time, verify that the fan kicks in properly when the engine is hot and stationary, and keep an eye on the temperature gauge in town and in traffic jams, where overheating tends to happen.
• ✓On an air-cooled motorcycle, keep the fins clean and avoid letting the engine idle for long periods in hot weather: moving airflow is its main source of cooling.