I have a 1995 Seville STS with the 4.6 Northstar. It was overheating,so I put in a new thermostat, heater core, water pump, and radiator. But that's not my concern anymore. Now when I start it up the exhaust manifold turns cherry red and starts smoking. Can anybody tell why,and what can I do to fix this?

 

Sounds like your catalytic converter is stopped up....that would explain the overheating, AND the red manifolds.
How long does it take for the manifolds to turn red? If it's immediately, I'd say it needs a new cat. If it takes a few minutes, then it may be running VERY lean, which would also damage the cat(s).

 

to complicate matters, if the engine was running rich, raw fuel was being dumped into the cat which would also cause a failure.

check codes, report back ...



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wow. i have the same problem. replaced thermostats, water pump, spark plugs, coils throttle body and it still glows red after about 5 minutes. BTW this is not a cadillac but a nissal altima 2.5s

 

I was a factory service rep for Nissan (Calsonic actually) and I noticed on the company car I drove (Nissan Stanza) it was not unusual for the exhaust manifold under the heat shield to glow red hot after driving normally on the highway.