Modern coolants contain additives that coat the inside of the cooling system to prevent rust and corrosion. In time these additives become depleted or worn out. A worn out antifreeze/water mixture can cause severe corrosion and rust buildup inside your vehicle's engine coolant passages. This causes a contamination of the mixture that results in abrasive particles, electrolysis of metal parts, and acid formation. Radiators, heater cores, and cylinder coolant jackets can become clogged and restrict proper cooling. Electrolysis, acidity, and abrasion can etch, dissolve, and wear through radiators, pump impellers, heater cores, gaskets, and core plugs. Failure of the cooling system can cause the engine to overheat. Overheating will stretch head bolts and can warp the cylinder head and other engine parts.
Follow the manufacturer's recommended coolant change intervals. This may vary between 2 to 5 years, and 30,000 to 100,000 miles. If the coolant becomes contaminated or acidic before the next scheduled change, replace it without waiting, and correct any problems that may have caused any failure. If any major parts are replaced in the cooling system (ie Water Pump, Radiator) new coolant is required to provide fresh additives to protect the new part.
Antifreeze / Antiboil
Antifreeze is always needed, even in warm weather when water won't freeze. The antifreeze also has anti-boil properties that raise the boiling point of the coolant mixture. The internal temperature of the engine reaches temperatures above the boiling point of plain water. The most common mixture rate is 50% antifreeze and 50% water.