Common problems of radiators are clogging, low coolant level, and coolant leakage from burst cooling system hoses, gaskets and seals. Internal corrosion and accumulated deposits can inhibit coolant circulation. When coolant circulation falls below design specifications the coolant temperature rises. At higher temperatures the cooling system is less able to absorb heat and overheating can result. To do its job efficiently, a radiator needs the help of a cooling fan. A malfunctioning electric cooling fan, an eroded or loose water pump impeller, or a slipping fan clutch can all result in radiator overheating.
A malfunctioning thermostat frequently becomes the cause of engine overheating. The thermostat is a coolant valve designed to keep the engine temperature within normal range. A thermostat that fails to open properly reduces coolant flow, which can result in an overheated engine. A stuck thermostat can be caused by fatigue, corrosion or clogging.
Radiator problems can be caused by an inadequate number of tubes in the radiator core (following removal of damaged tubes), by radiator additives that clog tubes and by leaky upper and lower tanks. Loose radiator tube fins can also contribute to overheating. Fins that have poor contact with their tubes transfer less heat to outside air. Dirt, bugs and debris stuck in the radiator exterior can block air flow through the core, thereby reducing heat dissipation.
A collapsed lower radiator hose and a malfunctioning radiator cap can each cause overheating. A broken overflow pipe can cause the radiator coolant level to fall below normal, and a broken or missing baffle plate can cause the water pump to push coolant into the overflow pipe and out the radiator. Sometimes the rear bearings in older water pumps can introduce grease into a cooling system, where it contributes to tube clogging.
Tip: When refilling the cooling system be sure you fill it completely. Air in the system will interfere with coolant circulation, thereby reducing cooling efficiency. If the cooling system has no air bleeder valves, you can temporarily loosen a heater hose to purge the air.