If you're riding between 10 and 20 mph in low gears with highish engine revs, then there will be a lack of airflow through the radiator relative to the heat generated by the engine. If you stop and idle an already hot engine, it will get hotter still needing even more assistance from the fan. The slow speed for an extended period maybe why the fan is runnning more than normal?

Can you be more specific? When you say "all the time", do you mean quite literally all the time? Like, it never cuts out at all?

The fan should switch on at 102C and turn off when the coolant temperature drops to 95C. You can run a full diagnostic fan check through the diagnostic mode in the dash. Have you downloaded the service manual? It's all explained in there.

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