Mark VII V8-302 5.0L HO (1986)
Exhaust Heat Control Valve: Description and Operation
Exhaust Heat Control Valve
The purpose of the exhaust heat control valve, is 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 currently available; the bimetal spring type and the
vacuum actuated type.
Bimetal Type
The valve is normally in the closed position engine cold and not running to divert exhaust gases to the intake manifold riser pad. When the engine is
started, the heat from the exhaust gases actuates the bimetal spring which opens the valve. As operating temperatures are reached, the valve will remain
open. The valve, when cold, will also open at high engine speeds, due to the action of the exhaust gas on the unbalanced valve plate.
Vacuum Operated
The vacuum operated heat valve functions as follows:
^ When the engine is started, the valve is closed by intake manifold vacuum acting on the vacuum motor.
^ The valve will stay closed until one of two conditions occurs:
1. When the engine coolant temperature reaches a predetermined value, the vacuum supply to the heat valve is shut-off by a temperature sensing vacuum
switch and the heat valve opens.
2. When the engine speed/load condition causes a drop in intake manifold vacuum below a specific value, the heat valve opens.
