Intake Manifold Getting Hot?

[Scott V.]

Hi,

My friends 1959 intake manifold has developed a hot spot which has actually burned the paint off (please see picture). Is there a passage that could be blocked. Would appreciate any advice on what this is and how to fix it.
20250228_144344.jpg
Thanks,

Scott

[Gary C.]

Scott,

Maybe install manifold heat blockers. See attached 1956 TSB.

Also, you might want to wire your exhaust heat riser open.

Gary
....

[Arland D.]

Once upon a time Dennis Clark and I did this to my 67 Buick 340 engine and it became very cold blooded and took a long time to warm up and run like it should. During the summer it was good for driving in high heat and heavy traffic with the A/C on.

[Don H.]

I would consider that normal.

[Duke W.]

Check the heat riser valve with the engine cold. Light force on the weight should cause it to rotate down. For normal summer driving I recommend you wire it open.

I tried blocking the heat riser on my SWC's 327/340 back in the seventies... figured I didn't need it in California and had no intention of ever driving it in "winter conditions" again.

Driveabiluty was TERRIBLE! The engine had to be running for at least 20-30 minutes before the horrible stumble on clutch release went away unless I slipped the clutch excessively. The CR trans and 3.08 axle was certainly no help.

I cut shims out of, IIRC, .010" thick 304 stainless steel sheet stock. Since I wasn't sure blocking the heat riser would work out well I bent the top ends over about 90 degrees so I could pull them out if I had to. I recall I drove the car maybe three times from a cold start, and just couldn't stand it, so I loosened the manifold bolts and was able to pull the shims out with needle nose pliers, re-torqued the manifold bolts, and it sealed up.

It's a good idea to block the heat risers on a dedicated race car, but makes a carbureted engine very cold-blooded.

I know the WCFB and AFB carbs on 250 and 300 HP 327s have a phenolic spacer that acts as an insulatior... don't know if 283s have such, but check your AIM. Even if such was not OE, consider installing the one from the WCFB-equipped 327/250. I considered using the 327/300 insulator on my 327/340 (was not OE on the 340), but then I would have had to fab new a new choke tube and fuel pipe to the carb and I wasn't sure there was enough hood clearance to I tabled the idea and just dealt with the occasional fuel percolation problems.

Duke

[Joe L.]

Scott,

Maybe install manifold heat blockers. See attached 1956 TSB.

Also, you might want to wire your exhaust heat riser open.

Gary
....

Gary-----


If the intake manifold exhaust cross-over passage is blocked, the heat riser valve MUST be wired open or otherwise eliminated.

[Scott V.]

Thanks everyone for the responses. We'll start by checking the heat riser.