Now I have a new issue. From a cold start the engine warms up to about three-fourths normal operating temperature, then cools down to cold while still driving. Of course I parked it immediately. Let it cool down completely, checked fluids, drove it and it did the same thing. Checked coolant level again. It is full. I have a new thermostat and water pump in the engine. The heater also behaves the same way.
To me, it acts like the heater core is plugged, but the temperature gauge shouldn't creep down to the cold side. If anything, it should get warmer (or overheat) if the coolant isn't flowing properly.
Thanks, Darin