Note. On vehicles equipped with the Delco Loc II audio system, be sure to disable the audio system interlock before doing any work to disconnect the battery.
All vehicles covered in this manual have a closed cooling system where coolant circulation is controlled by a thermostat. A forced coolant circulation pump mounted on the engine block circulates coolant through the engine and radiator. Coolant flows around each cylinder and returns to the radiator. Molded fluid passages wrap around the intake and exhaust manifolds, run near the spark plug areas, and close 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 cooling efficiency of the fluid in the radiator. If the pressure in the system exceeds the set pressure of the plug valve, the excess system pressure opens the spring-loaded valve and allows the coolant to escape through the hose into the expansion tank. As it 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 "closed system", since the coolant that has escaped through the valve is stored and reused.