Manifold Heat Control Valve - stuck close

If your valve refuses to rotate on its own when you rev the (cold or cool) engine, there's something the matter with it. The one and only correct stuff to lube the valve is Chrysler P/N 4318039AC. Do not substitute.

There is no "open" or "closed" on a Slant-6 heat riser, there is "heat on" and "heat off". A heat riser valve stuck in the heat-on position will cause bìtchy hot idle/hot start problems, but no, it will not start a fire. A removed/disabled/blocked off heat riser is not a good idea, either.

The rectangular-counterweight heat riser valve used up to '70 swings over into the heat-off position and stays there once it warms up. The round-counterweight valve used from '71 up will return to the heat-on position at idle and low engine speeds until it is extremely hot, so it's normal to go for a drive, come back, pop the hood, and see it still returning to the heat-on position until you rev the engine. Since all Slant-6 exhaust manifolds fit all Slant-6 engines, it's entirely possible (and increasingly common) to see a round-weight valve even on a pre-'71 engine.