For a 3D-animation look at how coolant flows through the engine and cooling system of a car, watch this video. I One of the most commonly neglected maintenance procedures is changing coolant, or antifreeze. On average, for every hour an engine runs, about 7,500 gallons of coolant circulate through its cooling system.
Coolant usually contains ethylene glycol, along with rust inhibitors.
The life span of these chemicals is about two years, so about every 24,000 miles a complete coolant flush and change is recommended. Otherwise rust and impurities may build up and clog the system, or the antifreeze may become ineffective. If you ignore the coolant, a severe freeze could crack your engine block. Changing the coolant doesn't mean simply draining the radiator and refilling it. A complete coolant change means back-flushing the entire system, then adding new coolant.