There have been some questions about the heat riser valves.
On my 69 Lebaron I had locked the heat riser valve open because of a rattle.
I just did an experiment to check the function of this valve. Upon removing the hose clamp that I have to hold the valve open, the valve rotated clockwise about 100 degrees to rest against the stop.
I started the car and the valve began to bounce to about 10-15 degrees back from the stop in a counter clockwise direction. I could hear it rattling. As the engine warmed the RPM increased to probably about 1500 RPM, but the position of the valve did not really change. It was within a few degrees of being closed. As the engine warmed more and I kicked off the fast idle, the valve bounced less, but was still almost closed. I had my son get in the car and hit the gas. He had to give it quite a bit of gas (> 2000 RPM) and then the valve would open very quickly about 45 degrees. It would slam shut as soon as the engine slowed, again to within a few degrees of being closed. The slamming shut was accompanied by the rattle.
From this I conclude:
1) Rotation of the valve counter clockwise opens the valve. Clockwise rotation closes it.
2) The valve has just over 90 degrees of rotation.
3) The valve is very close to being closed at anything below about 1500 rpm or higher irrespective of engine temperature.
4) On my car the valve is open when the counter weight is at the top pointing forward and closed when the counter weight is to the front of the car pointing down or a little bit back.
Fred Joslin
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