Coolant is made up of water, glycol and supplemental cooling additives. Additives are a small portion of the mixture but they have a big affect on coolant application. There are three basic types of coolants in use today, and each is defined by its corrosion inhibiting additives.
Water and glycol flowing through the cooling system can quickly cause engine damage. This basic mixture eats away at vital engine components, while also creating rust and scale. Tiny bubbles may also form, causing pitting throughout the cooling system. This is referred to as cavitation.
Corrosion inhibitors defend against these problems by bonding to the metals of the cooling system. This provides the engine components with a protective layer.