is it overheating on a logging system where you can read actual temp numbers? i had a bad sensor once that would show all kinds of different readings, but with some logging software i found out it was the sensor and not the motor.
if there was trapped in the system that can also cause it to read high because he air trapped will be hotter then the coolant that is flowing through. when you got to the light there still could have been air in the system and its hitting the air pocket at the sensor. id say burp and fill the system one more time.