The cooling system uses a water/antifreeze coolant to carry away excess energy produced in the form of heat. The cylinders are surrounded by a water jacket from which the heated coolant is circulated by thermo-syphonic action in conjunction with a water pump driven from the output shaft front end. The hot coolant passes upwards through the coolant pipe stub and top hose to the radiator which is mounted on the frame downtubes to take advantage of maximum air flow. The coolant then passes across the radiator core. where it is cooled by the passing air, through the thermostat and bottom hose and then to the water pump and engine where the cycle is repeated. A thermostatically-controlled electric fan is fitted behind the radiator to aid cooling. A wax pellet type thermostat is fitted in the system to prevent coolant flow through the radiator when the engine is cold, thereby accelerating the speed at which the engine reaches normal working temperature; coolant is routed instead from the coolant stub through a bypass hose to the thermostat housing and bottom hose.
The complete system is partially sealed and pressurised, the pressure being controlled by a valve contained in the spring loaded radiator cap. By pressurising the coolant to approximately 14.5 psi, the boiling point is raised, preventing premature boiling in adverse conditions. The overflow pipe from the radiator is connected to an expansion tank into which excess coolant is discharged by pressure. The expelled coolant automatically returns to the radiator. to provide the correct level when the engine cools again. A valve in the tank filler cap opens at the required level of outside pressure (relative to that inside the tank) to admit air as necessary.
Next Section: 2. Cooling system: draining