Exhaust manifold heat riser weight?

Started by DENNIS P NOLAN, February 04, 2024, 06:53:09 PM

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A lean mixture can cause the car to run hot and as the mixture takes longer to burn some of it will be burning in the exhaust manifold heating it up.

Another thing that can get the exhaust manifold hot is burnt exhaust valves.

So do a compression check and verify your carburetor mixture is correct. And, for that matter, that you ignition timing is correct.


Hello Plymouth Family- I ran the car just now- and possibly the cover was stuck??
it now rotates by itself 90 degrees-however the exhaust manifold glows red...not sure that
in and of itself is correct? but the heat riser mechanism cover moves-when the car is running-Thank you!!


Thanks Todd-
There is a cover and the cover rotates ...like 90 degrees-
however-when the car is hot- that cover is in the same place- I will
try to manually hold it open and then see what happens-Like a wrench or
piece of metal just to try that-
As usual I appreciate your info...


I am not sure when they changed. The early cars had a cover over the spring and a little weight lever with a knob shaped end. I think later cars just used a weighted cover.

A long while back I was able to get the thermostatic spring and weight from, if I recall correctly, Antique Autoparts Cellar (a.k.a. Then and Now Automotive). You may want to check with them.

For 1933 and maybe other years the Deluxe model had the thermostatic spring while the business or standard versions simply had a set screw setup where you changed the heat riser position each season. So it should not be a problem if you simply lock the heat riser in the hot position.


I have a 39 P-8-
I replaced the exhaust manifold a few years ago-
When I started the car today- the Exhaust manifold was glowing!!
I noticed there is no 'weight' to rotate the spring (or the spring
rotates the weight)-can't I 'rig' this open? when the car is cold-
the spring closes this correct-? or in this case it just STAYS closed-
thus the heat that the manifold exhibits- as it heats up it is supposed
to open and that is done with the weight? Missing piece-the weight-
to hold it open- Thoughts?

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