'59 Plymouth Forum

This might seem like a silly question but what does this valve do ? Only one side has one and mine appears to be seized solid in the open position. Does it need to be functioning ?

Guy; This might seem like a silly answer... The heat riser valve you are refering to is for early fuel evaporation during engine warm up, by directing Hot exhaust gasses through the bottom of the intake manifold.This helps the evaporation of raw fuel when the intake is too cool. This aids in less engine wear and a better a behaved engine ,ready to drive earlier.
The heat riser valve being stuck open is alot better than if it were sticking closed. It would be better if it were working. Fuel economy and driveability.

Yeah, when the engine is cold, the externally-mounted spring and counter-balance weight rotates that valve to the closed position. When the car gets started, warm exhaust gasses are deflected thru passges in the intake manifold, warming things up. When the heat at the valve reaches a certain point, the spring opens the valve and the exhaust is directed out the tailpipe.
Be careful un-seizing that valve, it can be broken! Use lots of penetrating rust dissolver and try to get the shaft to rotate a little bit at a time. Keep working it until it moves freely.

Now I understand. That's a great help - now just need to take a bit of care trying to get it moving. thanks