CCKW manifold heat control valve

[RANGER]

Your Exhaust Manifold will last longer if the Heat Control Valve is left in the "OFF" position year round. What happens is that with the valve in the "ON" position (Winter), or "MEDIUM" (Spring and Fall), a hot spot is created that tends in time to cause a crack at the center portion, which ruins your manifold. Leaving the manifold heat control valve in "OFF" position will minimize this tendency. As for affecting efficient operation of the Carburetor, it is not a problem as it just takes a moment longer to bring the intake manifold and carburetor base up to temperature.

Manifolds are very scarce and expensive, GM stopped making them over 20 years ago.