Why does the fan keep running after the motorcycle stalls?
2 Answers
The reason why the motorcycle fan continues to run after stalling is due to excessively high engine temperature. Excessively high engine temperature: At the moment of stopping, the engine coolant temperature is higher than the acceptable soak temperature for the engine. The vehicle's computer will automatically calculate the fan's operating speed and duration, thereby controlling the fan's operation automatically. Protecting the engine: The fan is installed behind the radiator. When activated, it draws air from the front of the radiator. The fan's operation is automatically started or stopped based on the water temperature conditions. The higher the engine temperature, the longer the fan runs after stopping. When the engine coolant temperature drops below the soak temperature, the fan shuts off, thereby protecting the engine and extending its service life.
When I first started learning to repair motorcycles, I was also puzzled by this issue. Later, my mentor told me it's a completely normal protective mechanism. After riding, the engine compartment is as hot as a steamer, so the system automatically keeps the fan running for a few more minutes until the temperature drops back to a safe level. This is especially true for water-cooled engines, as the radiator needs continuous cooling. As long as the fan stops within 10 minutes after turning off the key, it's fine. Of course, if the fan keeps running for half an hour without stopping, you should check if the temperature sensor is faulty or if there's insufficient coolant causing cooling failure. Once, while helping a fellow rider with diagnostics, we found that the fan relay was stuck, and replacing a small part solved the problem.