Figure 1-8. Coil spring-type thermostat

c. Operation (fig 1-9) The thermostat is located

between the engine water jacket and the radiator, usually

in the housing at the cylinder head, water outlet.

Automatic operation of the thermostat valve holds coolant

temperature within proper limits by controlling floe of

coolant through the radiator. When engine is cold, the

thermostat valve stays closed and shuts off practically all

circulation to the radiator. As the engine harms up, the

valve opens slowly, allowing some coolant to flow In actual

operation, the valve may move frequently to regulate

coolant flow into the radiator in accordance with variations

in heat output from the engine.

d. Thermostat By-pass. Cooling systems equipped

with a by-pass arrangement have coolant circulation within

the engine water jacket when the thermostat is closed.

The external-type bypass consists of short hose, pipes, oil

tubes connecting the cylinder head outlet directly with inlet

of the water pump. The internal-type by-pass provides for

coolant flow from the head directly back to the pump

Figure 1-8. Coil spring-type thermostat - cutaway view.

through passages built into engine water jacket.

CLOSED

OPENED

Figure 1-9. Thermostat operation

1-7