Function
The cooling system allows the engine to rise to full operating temperature when engine is started cold, but keeps the engine from overheating once engine reaches operating temperature. The thermostat opens when operating temperature has been reached, circulating coolant from the hot engine to the radiator to prevent engine overheating. The cooling system is pressurized, which raises the boiling point of the coolant, and allows more heat to be carried away from the engine.
Theory of Operation
The cooling system includes the following components: radiator, radiator cap, upper and lower radiator hoses, coolant pump, fan, thermostat, coolant recovery tank, drain hoses and drain valve.
When the engine is started cold, the thermostat is closed. The impeller type coolant pump pulls coolant from the cylinder head and through the bypass tube inside the water pump housing. The water pump then pushes the coolant into the cylinder block water jacket. The coolant absorbs heat from the cylinder walls, and is then pushed up into the cylinder head, and sucked back into the water pump. This provides a fast warmup period, as engine heat is retained and evenly distributed throughout the engine.
As the engine reaches operating temperature, 69.5—72.5°C (157—163°F), the thermostat opens, and the hot coolant from the cylinder head passes through the thermostat and into the top tank of the radiator. As coolant flows down through the tubes of the radiator core, heat is transferred from the coolant to the air stream being drawn through the core by the engine fan. When the coolant reaches the bottom radiator tank, it is sucked through the lower radiator hose and into the water pump, and pushed back into the cylinder block.
When coolant system pressure exceeds 88.3 ± 14.7 kPa (12.8 ± 2.2 psi), the spring in the radiator cap pushes open to allow coolant to discharge into the coolant recovery tank. As the engine cools after shutdown, a vacuum is produced in the cooling system, and coolant is drawn back out of the coolant recovery tank through a small valve in the bottom of the radiator cap.
Air is pulled by the engine fan through a removable debris guard on the front of the radiator, through the radiator and fan, and back over engine block. The engine fan belt drives both the water pump and the cooling fan.
An electrical coolant temperature switch is located in the thermostat housing. When the coolant temperature reaches 107—113°C (225—235°F), the coolant temperature switch closes, lighting the coolant warning light on the instrument panel. The light informs the operator of the high temperature condition.
The radiator can be drained with a drain valve on the lower right corner of the radiator. The engine block can be drained through the drain port on the left side of the engine near the front, next to the oil pressure switch. The coolant recovery tank can be removed and drained.