6-Cylinder Engines: Notes

The thermal vacuum switch is a normally closed switch which is sensitive to oil temperature. With a cold engine, below 150°F, TVS is closed which allows manifold vacuum to the actuator valve. Vacuum pulls the diaphragm in the actuator, closing the EFE Valve. This causes the hot exhaust gases to be routed to the base of carburetor. When oil temperature is above 150°F, the thermal vacuum switch opens. This stops vacuum to actuator. Without vacuum, a spring pushes actuator diaphragm to its at rest position and opens the EFE valve.