The radiator fan is a small electric fan mounted behind the radiator on liquid-cooled bikes. A temperature switch in the coolant, or the ECU, turns it on when the engine gets hot. Many scooters with air cooling use an engine-driven fan and ducting instead; that fan is part of the engine.
What it does
When the bike is moving, air flows through the radiator by itself. In slow traffic or at idle there is not enough airflow, so the fan pulls air through. It switches on at a set temperature and off again once the engine cools. Fan motors wear out, blades crack, and the switch, relay, fuse or wiring can fail. Water and mud reach the motor and plug.
Signs it is worn or failing
- Radiator fan does not switch on.
- Overheats in traffic but cools when moving.
- Temperature gauge high or warning light on.
- Fan runs all the time, or makes grinding noises.
When to replace it
When the motor does not run with power and earth fed straight to it, the blade is broken, or the bearings are noisy. Replace the switch or relay if the fan runs on direct power but not from its circuit.
What to match when buying
- Match make, model and year: blade size, mounting points, rotation direction and plug.
- Fan switches are rated for a switching temperature and thread; match the number on the old switch.
- Check the fuse rating for the fan circuit in your manual; never fit a larger fuse.
Fitting notes
- Home job: Test the radiator fan and its switch.
- Keep fingers clear: a fan worked by a temperature switch can start with the key off on some bikes.
- Seal the plug against water after testing: Clean and seal electrical connectors.