Radiator

The radiator is the heat exchanger of a liquid-cooled engine. The water pump sends hot coolant from the engine through thin tubes surrounded by fins; air flowing through the core takes the heat away, and the cooled liquid returns to the engine. An electric fan switches on when airflow is too low, for example in traffic.

Problems to watch for: rising temperature on the gauge, coolant leaks, a fan that does not run, or bent and blocked fins. On off-road bikes, mud and crash damage are common, so radiator guards are a sensible upgrade.

Check the coolant level when the engine is cold, use the coolant type the manufacturer specifies, change it at the service interval, and clean the fins gently with low-pressure water.