What could this Temp Gauge Electrical Gremlin be?
 

After the 930 warms up, the temperature gauge starts climbing higher than it is running, especially after running a while. This has a new numeric gauge & sending unit. I know it is not running at 250, because when I hit the window switch it will fluctuate the temperature. Also after it is turned off & turned to the on position it reads usually about 212 degrees. What could be causing the jump in harmony with the window switches? Ideas?