The cooling system is designed to bring the engine to the proper temperature and to maintain the temperature there. It does that by using internal engine temperature to heat the coolant. Conversely the radiator fluid (coolant) is cooled by air flow through the radiator. There are rows of thin capillaries in the radiator. When the vehicle isn’t moving, the cooling fan compensates by sucking air through the radiator.
In order to maintain the cooling system, the fluid needs to be changed about once every 2 years or 30,000 miles. Over time the coolant loses its ability to protect the multiple components in the engine and cooling system. As the fluid gets older the pH goes up and the nitrates go down. The pH and the nitrates are what protect the system.
Ironically, the radiator and cooling system are what provide the passenger interior with heat when needed. The heat in the radiator fluid goes to the heater core, then air is pushed over it on its way to the passenger cabin.