manifold heat control valve

[rays266]

is it true that a stuck manifold heat valve in the closed position can cause a /6 to overheat?

 

[BillGrissom]

Probably. The engine would be inefficient, which is one way to overheat. You can test for any exhaust restriction with a vacuum gage on the intake. Rev the engine and if you see a slow increase in pressure (loss of vacuum) at a constant rpm, that indicates a restriction.

 

[67 Power Wagon]

Stuck heat valve ONLY in the closed position tho....A stuck open one should allow the passageway to be unrestricted, right?

 

[rays266]

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.

 

[CichliDart]

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.

 

[cudajim]

Yup, closed is bad, mine is stuck open so it gives me no problems and I'm not about to "fix" it either.