Manifold Heat Valve
1. Unhook the thermostat spring from its anchor pin and check the adjustment.
2. Proper adjustment and hook up requires only 1/2 turn of the spring from its unhooked position to slip it over the anchor pin.
Note: Should this spring be distorted in any way it should be replaced.
3. Check valve shaft to make sure it is free in the manifold. If the shaft is sticking, free it up with kerosene containing a small amount of baking soda.
From chevy.tocmp manual
