Thermal Vacuum Valve: Description and Operation

NOTE: These valves were fitted from Engine # 8S57762 up to Engine # 8S64244.

Thermal Vacuum Valve:

Vacuum System:

A distributor advance thermal vacuum valve, located at right rear coolant manifold, senses engine coolant temperature and routes vacuum accordingly. (It is the valve with three connections, closest to firewall).

Vacuum System - Coolant Temperature Below 95 Degrees F:

When engine temperature is below 95° F (35° C), thermal vacuum valve connects top with middle port. This causes vacuum advance to be operated by throttle edge port vacuum via vacuum regulator. A delay valve prevents sudden loss or increase of vacuum when throttle valve is moved quickly. The vacuum regulator won't allow vacuum to be applied to the advance unit until the "carb" port receives vacuum signal.

Vacuum System - Coolant Temperature At Or Above 95 Degrees F:

Once engine temperature reaches 95° F (35° C), the thermal vacuum valve connects middle and lower ports. This allows vacuum advance to be controlled through the vacuum regulator.