- Check the routing and connection of all vacuum hoses.
- Attach a tachometer to the engine.
- Bring engine up to normal operating temperature. The engine must not be overheated.
- Note the engine speed when the transmission is in Neutral and the throttle is in the curb idle position.
- Disconnect the vacuum hose from the intake manifold at the temperature-sensing valve. Plug or clamp the hose.
- Note the idle speed with the hose disconnected. If there is no change in rpm, the valve is good. If there is a drop of 100 or more rpm, the valve should be replaced. Replace the vacuum line.
- Check to make sure that the all-season cooling mixture is to specifications and that the correct radiator cap is in place and functioning.
- Block the radiator air flow to induce a higher-than-normal temperature condition.
- Continue to operate until the engine temperature or heat indicator shows above normal.
If engine speed by this time has increased 100 or more rpm, the temperature-sensing valve is satisfactory. If not, it should be replaced.