Honda CX500 1978 Shop Manual page 237

COOLING SYSTEM
-
The cooling system consists of the radiator, reserve tank, thermostat, fan, water pump and water jackets that surround the
cylinders and cylinder heads. The water pump is driven by the camshaft and draws cool water from the bottom of the radiator
and pumps it through the water passage at the rear of the engine case into the water jacket of each cylinder. The coolant
circulates around the cylinder bores and is directed upward into the cylinder heads where it cools the combustion chambers,
valves, and valve seats. After cooling the cylinder heads, the coolant flows through the thermostat, if it is open, into the top of
the radiator. In the radiator, the temperature of the coolant is reduced as it dissipates heat t o the fan's air stream.
COOLANT FLOW
When the engine is cold, the thermostat bellow contracts and closes the valve. This causes the coolant t o circulate only in
-
the engine water jackets. Only a small amount of coolant is returned through the by.pass hose into the radiator, causing the
engine t o warm up quickly.
As the coolant warms, the bellow expands and the valve opens. This allows the coolant t o flow t o the radiator where it is
maintained at the desired operating temperature.
The radiator cap incorporates two valves, the relief valve and vacuum valve. The valve allows air and vapor or coolant t o
escape into the reserve tank if pressure exceeds that for which the system is designed, thereby maintaining a safe pressure in
the system. The vacuum valve prevents formation of vacuum in the system when the engine begins t o cool after it has been
shut off. A pressure drop in the radiator causes the valve t o open, allowing coolant from the reserve tank into the radiator.
The design prevents loss of coolant by evaporation except that through the breather in the reserve tank and eliminates
frequent refilling of the system.
Date of Issue: January,
1978
OHONDA MOTOR CO., LTD.
1 9 - 1