manifold heat control valve

Thanks Bill. I see so many overheating problems in here. Good radiators, proper thermostat, etc. all the usual culprits yet the overheating persists, usually at high speeds. This valve will blacken the plugs, rob performance, and is easily overlooked.

Had this happen on a 318 about 25 years ago. Ran horrible, blackened plugs etc.
Removed the manifold and removed the flapper, reinstalled, ran great.