Chevrolet Full-size Cars 1968-1978 Repair Guide

Manifold Heat Control Valve (Heat Riser)-1968-74



This valve is located in the exhaust manifold under the carburetor on in-line engines, and in either the right or left side exhaust manifold on V engines. It can be identified by looking for an external thermostatic spring and weight, and hinge pins that run through the walls of the manifold. Check the valve for free operation every 6,000 miles and, if it binds or is frozen, free it up with a solvent.

Certain early engines has the heat riser built into the manifold and could only be repaired by replacing the entire manifold.