manifold heat control valve

A few more scraps of info. My 65 Dart 273 has a round weight on the heat riser and the shaft moves freely. I don't know if original for V-8's. Will check the manuals. My 69 Dart 225 had the stamped steel weight. I recall there was a flat on the shaft that oriented it. Anyway, the weight fell off on the road. The round weight appears a better design.

The factory manual says to periodically spray the shaft with a special solvent (from dealer) to keep it moving freely. Has anyone tried getting it at a dealer today? WD40 or such is probably similar.

dartpower has the opposite problem of exhaust gas leaking past the shaft. I recall that when I did the "bolts in holes" fix, I coated the bolts with "muffler bandage cement", which I had lying around. It comes in the muffler repair kits in auto parts. You could probably also use "furnace cement" (Ace Hardware) or some of the copper anti-seize products. Maybe even high-temp RTV, but you pushing its limits. The shaft collar will probably seal after a while as carbon from the exhaust clogs the small passages.

The "heat on firewall" problem is probably due to an exhaust manifold leak. Start the engine cold and place your hands around it before it gets too hot. You should feel a puffing, and even hear it. If you catch it soon, you can often fix by just tightening the manifold nuts. Also check the intake-exhaust joint and the exhaust pipe flange. There are products to keep the manifold nuts from loosening, but are usually bolts so you must remove your studs first, which runs a risk of snapping a stud off, so wait until the heads are off someday. Your exhaust manifold may also have a crack. That is a problem with all 6-cylinder exhausts and even the heads. Mercedes six cyl diesels are notorious for cracked heads (5 cyls almost never crack), which is why people try to unload their over-heating station wagons on newbies, saying "maybe just a heater hose".