The engine coolant is circulated by a thermo-syphon, water pump-assisted system, and is pressurised. Pressurisation is necessary to allow the engine to operate at temperatures higher than the boiling point of the cooling water. The pressure is controlled by the springloaded radiator cap which effectively seals off the cooling system from atmosphere. When the system pressure reaches the rated pressure of the radiator cap, the spring is overcome; the internal portion of the cap lifts off its seat allowing steam to escape down the overflow pipe, thus relieving the pressure. When the engine is stopped and the system is allowed to cool, a vacuum is created in the cooling system. To allow for this, a vacuum valve is incorporated in the cap which will open and allow excessive vacuum to vent to atmosphere.
The cooling system comprises, the radiator, water pump (mounted on the front of the engine, it carries the fan blades and is driven by the fanbeit), thermostat and associated hoses.
The system functions by circulating cold water from the bottom of the radiator, up the lower radiator hose to the water pump where it is pumped around the water passages in the cylinder block.
The water then travels up into the cylinder head and circulates around the combustion chambers and valve seats. When the engine is at its correct operating temperature, the water travels out of the cylinder head, past the open thermostat, into the radiator top hose and so into the top tank of the radiator. The water travels down the radiator where it is rapidly cooled by the rush of cold air through the radiator core. As the radiator is mounted in the wheel arch, the fan pushes cold air through the radiator matrix. The water, now cool, reaches the bottom of the radiator, where the cycle is repeated.
When the engine is cold, the thermostat (which is simply a temperature-sensitive valve), maintains the circulation of water in the engine by blocking the passage from the cylinder head to the radiator, thus forcing the water to return to the cylinder block via a bypass hose. Only when the opening temperature of the thermostat has been reached, as shown in the Specifications, does the thermostat allow the cooling water to return to the radiator.