Why is coolant replacement important?

Advances in engine building and design, fueled by the never ending quest for more power and higher reliability resulted in engines loaded with aluminum, such as Engine blocks, cylinder heads, radiators and engine system components. Coolant provides corrosion protection required for the aluminum to survive. Coolant will also lower the freezing temperature but also raise the boiling point of the fluid. Coolant also prevents excessive silicate gel precipitation which may cause clogging of the cooling system. Over time, the corrosion inhibitors will be depleted and corrosion protection lost requiring coolant replacement.