why would my 1st catalaytic converter glow red. 1st one off the manifold on 2001 Toyota Solara

the car runs just a little hot . both fans run and work properly. if a/c is on the car does not overheat until you shut down. then you get a minor gurgling coming out of the head. It does not show any codes. have replaced radiator, water pump, thermostat. I have since then took the guts out of the thermostat so its free flow. Seems like it heat up very quickly from a cold start.

Asked by for the 2001 Toyota Solara