Single-Function for Heavy Duty Cooling

Valve is used to prevent engine overheating at high ambient temperatures. When coolant temperature is below 220°F, carburetor ported vacuum enters port "1" and is applied through port "D". This allows full ported vacuum to distributor. Above 220°F, port "1" is blocked and manifold vacuum enters through port "2" and connects to port "D". Manifold vacuum then controls spark advance. See Figure.