cars runs good, but exhaust manifolds get cherry red block is much cooler on 1994 Buick LeSabre

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I have a 3800 v6 we have done a compression test all cylinders are at 150 psi. cooling system pressure check holds 18lb. no oil in coolent or coolent in oil. engine runs smooth, and starts easy. Runs well and not overheating running at normal temp. cooling fans working. How ever the exhaust manifolds get very hot. much hotter then the engine and when you hold the gas to about 2000rpm they turn cherry red. starts close to the heads and moves down the exhaust. Any one ever have this problem?
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(1) Comments
The exhaust manifold does get very hot but if it is glowing cherry red it could be a restriction in the exhaust/ restricted catalytic converter, it could be a lean air fuel mixture, or retarded ignition timing all of the above should cause a loss of power or fuel economy.
Patrick, thanks for the response. We removed the exhaust to see if it made a change, no still the same. We did a smoke test for vacuum leaks, none found. The engine has good power at all ranges and no dead spots when given gas. at idle it seems to be ok. But if you increase the engine rpms to 1500 or above the exhaust manifolds get over 1000 degrees, the block is still cool enough that the thermostat hasn't opened around 136 degrees. as it reaches temp to open it does and cooling fans come on when called for by the ect. This one has me a little loopy not sure what I,m over looking?????
I agree with the lean fuel mixture or cat converter plugged. I have seen both cause this issue, with the majority being converter.
The only reason the exhaust manifolds can be turning red - when everything else is working properly - is that they are made of thinner metal and not the solid cast iron used in older manifolds. Thinner metal cannot conduct heat fast enough. Make sure nothing that can melt is near and definitely not touching the manifolds.