Coolant temperature sensor could be bad.
Your engine has two, one for the PCM, one for the gage.
Gage sensor should read 16.0 ohms hot and 275 ohms cold. Obviously , those values will vary, showing whatever the ambient/actual temperature of the sender is at that moment. If you are going to test it, just immerse in pans of cool / hot water while the meter is connected.
Or, replace the sensor. The one you are looking for has the red wire with a white stripe (RD/WH).