Found the problem with my car overheating.
Stupid engineers thought it might be a good idea to use glue to hold 2 metal parts together in a area full of hot water. And when it fails, the smaller metal part then blocks proper water flow to the radiator. Since the radiator port is about opposite of the heater core port, it explained why it would cool the car by keeping the heater on.
Now, why I call the engineers stupid, It occurred to me after seeing the failure mode that if they had attached the disc to the impeller blade of the water pump, the machining would have been just as easy, and the impeller would be cast as one component easy enough with fewer failures. Might not seal as complete, and lose a little efficiency but it would be less likely to fail.
Of course I should not be too annoyed, I don't think the glue gave way till I had a severe overheating problem. That problem was due to the water pump belt breaking. 147k miles for a belt was pretty good. The part that is annoying me is that the pump is available at the local stores, but the housing that has the glued part seems to be a dealer only part. So my Sunday afternoon attempt to fix the car turned into a multi day repair job due to waiting till business hours to get the parts.