Thermostat: Description and Operation

DESCRIPTION AND OPERATION
1. When the coolant is cold, the water thermostat is in the closed position and the coolant flow is limited to the:
a. Cylinder block.
b. Cylinder head.
c. Intake manifold.
d. Heater system.
2. As the engine coolant temperature increases, the water thermostat opens allowing a portion of the coolant to pass into the radiator.