The most often replaced cooling system components include the coolant (antifreeze), water pumps, thermostat, hoses and belts.
Coolant has a limited service life, typically five years or 150,000 miles, whichever comes first which usually means changing the coolant every five years on most vehicles. Coolant also should be changed when replacing a water pump, radiator or heater core, especially if internal corrosion caused any of these parts to fail.
Antifreeze should be mixed in equal parts with distilled water (never ordinary tap water). Pre-mixed 50/50 coolant eliminates the guesswork and is ready to use. The type of antifreeze that is required will vary depending on the application. Coolants are formulated to meet the specific requirements of certain auto manufacturers (Ford, GM, Chrysler, Asian and European), or to be compatible with all makes and models (“universal” coolants).
Overheating can be caused by a sticking thermostat, a bad water pump or a coolant leak anywhere in the cooling system or engine. Replacement thermostats should have the same temperature rating as the original. A new thermostat housing also may be needed if the old one is corroded or leaking.
A water pump may need to be replaced if the shaft seal is leaking, the shaft bearing is worn, or the impeller inside the pump is loose or damaged. Other parts that will be needed include water pump gaskets, coolant, and thread sealer for mounting bolts that extend into cooling jackets. On older, high-mileage vehicles with a belt driven cooling fan and fan clutch, replacing the fan clutch also is recommended to reduce the risk of overheating.
Radiator and heater hoses deteriorate with age and should be replaced on high-mileage vehicles when changing other cooling system components. New clamps also are recommended.
Small radiator leaks can sometimes be repaired with cooling system sealer, by soldering (if the radiator is copper/brass) or by sealing with epoxy (aluminum radiators). But major leaks, internal corrosion or damage usually require a new radiator. The dimensions of a replacement radiator (height, width and thickness) must be the same as the original, and there also must be hose connections in the same locations. Radiator caps should be pressure-tested and replaced if they fail to hold their rated pressure. Replacement caps must have the same pressure rating as the original.
New belts are needed if a belt is worn, making noise, frayed, cracked, glazed or contaminated with oil or grease. Replacement belts must be the same width and length as the original. A new automatic belt tensioner is also recommended for high-mileage vehicles.