Thermal Vacuum Valve: Testing and Inspection

PROCEDURE
To test the valve, proceed as follows:

1. With engine at operating temperature, connect a tachometer to the engine.

2. Note engine idle rpm with transmission in neutral.

3. Disconnect the vacuum hose from the intake manifold at the temperature sensing valve and plug the hose.

4. If idle speed does not change when hose is disconnected, the valve is acceptable to this point. If idle drops 100 rpm or more, valve must be replaced.

5. Reinstall vacuum line then cover radiator sufficiently to raise engine coolant temperature above thermostat setting.


NOTE: Be sure all-season coolant is up to specification and exercise caution so that the engine does not become unduly overheated.


6. Continue to run the engine until the high temperature lamp comes on or the temperature gauge reaches the high end of the band. At this point, the engine idle speed should increase by approximately 100 rpm. If it has not, the valve is defective and must be replaced.