EFE Valve: Description and Operation

Exhaust Heat Control Valve:

The Exhaust Heat Control Valve is used to divert hot gases from the exhaust manifold to the intake manifold riser pad. Heat is transferred from the exhaust gas to the riser pad, which in turn heats the incoming fuel/air charge. There are two types of control valves; the bimetal spring type and the vacuum actuated type.

BIMETAL TYPE
When the engine is cold and not running the valve is normally closed to divert exhaust gases to the intake manifold riser pad. After the engine is started and the heat from the exhaust gases actuates the bimetal spring which opens the valve. When operating temperatures are reached, the valve will open. The unbalanced valve plate will enable the valve to open at high speeds even with the engine being cold.

VACUUM OPERATED
After the engine is started, the valve is closed by intake manifold vacuum applied to the motor. The valve opens after satisfying these conditions:
1. When the engine coolant temperature reaches a set value, vacuum is shut off to the heat valve by a temperature sensing vacuum switch.
2. Any drop in intake manifold vacuum (a specific value) caused by high engine speed or load.