Engine Cooling System

All models covered by this Manual are equipped with a pressurized engine cooling system with thermostatically controlled coolant circulation. The rotary-type water pump is mounted on the engine block and circulates coolant through the engine's cooling passages. The coolant flow surrounds each cylinder in the block and is directed to the rear of the engine. Cooling passages cast into the block and cylinder head provide effective cooling of the intake and exhaust ports, spark plug areas and exhaust valve guides.

A wax-pellet thermostat controls engine operating temperature during warm-up. During the first minutes after a cold engine is started, the thermostat remains closed, preventing coolant circulation through the radiator. When the engine reaches normal operating temperature, the thermostat valve opens, connecting the radiator to the cooling circuit to provide maximum heat dissipation from the coolant.

The cooling system is sealed and closed by the radiator cap, which is designed to withstand a specified positive pressure. This raises the boiling point of the coolant and, accordingly, improves heat dissipation through the radiator. When the internal system pressure exceeds a specified value, the spring-loaded valve disc of the pressure relief valve built into the radiator cap lifts off its seat, allowing excess coolant to flow through the overflow hose into the expansion tank. As the system cools, coolant is automatically drawn back from the tank into the radiator.

Coolant is added to the system through the filler neck of the expansion tank, which also acts as a reservoir that accumulates the excess coolant displaced from the radiator.

Due to these design features, this cooling system is called a closed system, since no functional loss of coolant occurs.