GM Chevy Mid-Size Cars 1964-1988 Repair Guide

Manifold Heat Control Valve (Heat Riser) 1964-74


This valve is located in the exhaust manifold under the carburetor on inline 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, along with 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 have a heat riser built into the manifold, which can only be repaired by replacing the entire manifold.