Note: On vehicles equipped with the Delco Loc II audio system, be sure to disable the audio lock before performing any work that involves disconnecting the battery.
All vehicles described in this manual have a closed cooling system, the circulation of coolant in which is controlled by a thermostat. A forced circulation pump mounted on the engine block pumps coolant through the engine and radiator. A stream of coolant passes around each cylinder and returns back to the radiator. Molded fluid passages flow around the intake and exhaust manifolds, near the spark plug areas and next to the exhaust valve guides.
The thermostat is connected to the upper radiator hose. Before warming up, the thermostat closes the circulation of coolant through the radiator. As the engine approaches normal operating temperature, the thermostat opens and allows hot coolant to pass through the radiator where it is cooled before returning to the engine.
The radiator cap has a valve that raises the boiling point of the coolant and increases the efficiency of cooling the liquid in the radiator. If the system pressure exceeds the set pressure of the plug valve, the excess system pressure opens the spring-loaded valve and allows coolant to escape through the hose into the expansion tank. As the coolant cools, excess coolant is automatically sucked from the reservoir back into the radiator.
The expansion tank also serves as a container into which fresh coolant is added to maintain the required level.
This type of cooling system is known as a "closed system" because the coolant that escapes through the valve is saved and reused.
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