1956 Cadillac intake manifold issue

[carguyblack]

I am working on a 1956 Cadillac for a friend and noticed something odd that isn't happening on my personal car of the same year. The intake manifold in the middle on both sides is just cooking hot and has burned the engine paint off of it. Mine doesn't do that. The car seems to run fine but it is just molten in those 2 areas pictured. Any idea why that's happening and is it a severe problem indicated by that?
Thanks for the input.
Chuck

[The Tassie Devil(le)]

Could possible be that the exhaust butterfly where the Exhaust Manifold joins the Engine Pipe is stuck in the closed condition, thus pushing all of the exhaust gas from that side, out and under the carby to the other side.

Bruce.

[Roger Zimmermann]

On my cars, I have the same situation. Even with a good functioning heat riser, that exhaust passage under the carb is very hot, burning the paint. On your car, you may have gaskets sealing the intake manifold to the heads with are closing this passage. This is done mainly to reduce the vapor lock issue  as less heat is generated under the carb.
One way to check it: do you have the heat riser at the LH exhaust manifold? Compare also that heat riser with the car you are working on. The heat riser must move freely by hand with a cold engine.

[Lexi]

That is actually par for the course as the hot exhaust eats the paint off. My engine paint burned off there within a month or so after rebuild and painting, (Hirsch paint used). Some guys plug the intake manifold holes to reduce the heat and lessen the chance of vapor lock.

On a side note, it looks like your throttle rod is installed backwards. I drove my car 8 years before I noticed it. On page 12-58 of the shop manual there is a diagram that shows the rod entering the throttle relay plate hole from the inside, (carb side) rather than the outside as in your case. You can remove and flip it as it is threaded at the other end at the fire wall. May need to re-check your idle and TV rod.  Clay/Lexi

[cadman56]

Lexi is correct.
Throttle rode should be on fender side of throttle plate/bracket with the big curve dropping down.

[carguyblack]

Good catch Clay and Larry! My personal car is correct but this convertible was put on wrong by someone else. I was only doing the paint and body work so I never noticed. The only reason I asked about the manifolds is because when we checked under the hood after driving the car home from the shop to check for leaks, that's when I noticed the white hot manifolds and thought that was not quite kosher.
Chuck

[Lexi]

No problem Chuck. Does it really matter what side the throttle rod enters that plate's hole? Probably not, BUT as it appears that your return spring is of the stubby "fat boy" type, (with a short lead?), which looks like it is hooked on the inside of the rod; there is the danger of the spring making contact with the carburetor's secondary throttle linkage. My guess is that is why the shop manual shows it mounted from the other side which gives more room for the spring to clear things, if so connected. It is also easier to get at when mounted as per the shop manual. My spring and set up looked like yours until it got caught on the carb and I found myself speeding along without my foot on the accelerator. Not good. That is when I found out mine was connected wrong. Safer to move them which is what I did. Clay/Lexi

[TomJudd]

Fix or remove butterfly, or you will eventually destroy cylinders/valves on 3 4 5 6 cyls. I removed mine, I will never worry. You can not tell.

[5390john]

Might want to consider removing the exhaust butterfly valve and replacing the intake manifold gaskets with new gaskets that have the center exhaust port blocked. That way, no exhaust gases circulate through the intake manifold under the carb. Keeps the carb LOTS cooler, doesn't bake the paint off the intake manifold, and helps prevent vapor lock. Gaskets available from Olson's.
John Adams

[carguyblack]

Thank you everyone for your sound advice. I continue to pass these all back to the owner of the car for his decision. Blocking the exhaust through the intake certainly sounds wise as excessive heat always seems to be the issue with this year car.
Chuck

[dplotkin]

Keep in mind that Cadillac designed its exhaust crossover for a reason and disabling it may lessen other troubles but it will effect running while stone cold. It it wasn't necessary to run as a Cadillac should it wasn't on the car.

Dan