A heat exchanger is a component of cooling system that is responsible for transferring heat from the engine coolant to the outside air. It consists of a network of tubes and fins that allow hot coolant to flow through while exposing it to cool air, thereby lowering its temperature. The cooled coolant then circulates back into the engine to prevent overheating. Heat exchangers are critical components in heavy-duty trucks as they ensure optimal engine performance and prevent damage due to excessive heat build-up. Proper maintenance and replacement of damaged or worn-out heat exchangers are vital for maintaining the longevity and efficiency of a truck's cooling system.