Sounds like a temperature dependant/time dependant short circuit in the temperature sensor circuit... here is why......
In the following link,
http://www.neon-owners.org/neon/tech...97/EPL_TAB.PDF
Refer to EPL_8W.PDF
Page 8W-30-7
The temperature sensor shares a ground with the cam sensor, the crank position sensor and the battery temp sensor.
You might unplug the sensor and see what happens just to confirm the fault.
Refer to EPL_7.PDF page 7-7
High gage temperature trouble shoot (not too helpful)
Refer to EPL_8E.PDF page 8E-7
Temperature gage test (a side issue)
Most importantly:
Refer to EPL_8D.PDF page 8D -15 and 16
Engine coolant temperature sensor check/removal and installation (diagrams included)