Chevrolet 1956 Truck Operator's Manual page 36

Manifold Heat Control Valve. The manifold heat control valve
on 6-cylinder engines is located on the inside of the exhaust
manifold and is operated by the thermostatic spring, the center
of which is attached to a slot
in the valve shaft and the
outer end bears against a
stop pin on the manifold.
When the engine is cold
the valve is in the "heat-on"
position as shown in the left
half of Figure 42, and the hot
exhaust gases are directed
against the center of the in-
Fig. 42-Ntanifald Heat Valve-
take manifold. As the engine
6
Cy/.
Engine
warms Up, the thermostatic spring moves the valve
to
the
"heat-off" position as shown in the right half of Figure 42 and
directs the exhaust gases away from the center of the intake
manifold.
This thermostatic control results in maintaining the proper
temperature of the incoming gases under all operating condi-
tions.
The tension of the thermostatic spring is very important.
When it is too tight the heat will not be turned off the intake
heat riser as the engine warms up, with the result that the
incoming g!lses will be expanded several times greater
in volume than in normal
operation and it will be im-
possible to get a full charge
of gas and air into the
cylinders
The manifold "heat con-
trol valve on 265 cu. in. V-8
engines is located
in
the
right manifold exhaust pipe
flange (fig. 43). In the "heat
on" position, back pressure
Fig. 43-Ntanlfald Heat Valve Thermostatic
forces the hot exhaust gases
Contro/-265 Cu. In.-V-8 Eng;ne
from the right exhaust manifold, through the intake manifold,
and bottom flange of the carburetor, to the left manifold.
The manifold heat control valve on the 322 cu. in. V-8
engine is located in the left exhaust manifold.