Re: Heat Riser problem

Posted by BH On 2007/8/16 12:27:53

IIRC, the electrically-heated thermostatic choke coil was a replacement for the tube on earlier cars (like our Packards), through which heated air was drawn across that bi-metal coil. The air drawn into that tube was heated by the flow of exhaust gas passing through the exhaust crossover passage in the intake, but that only happens when the manifold heat valve is closed. Heating the choke coil causes the choke valve to be unloaded, but that force is counterbalanced (at least in our Packards) by vacuum applied to a piston in the choke housing (via an internal passage).

Yet, heating the choke was a secondary function; the primary purpose of that exhaust crossover passage was to heat the intake manifold so vaporized fuel wouldn't condense back into liquid following a cold start.

Of course, I am talking from a perspective of V8 experience, in response to Owen_Dynetos' post, and drifted from an initial offering of info on chemicals to free and lubricate the heat valve. How it all works on an old straight eight is beyond me, but the underlying reasons for having the heat valve still apply.