It sounds like a bad Temperature Sensor or the Gage It's self.
Try replacing temperature sensor
If the engine temperature gauge on your 1996 Geo Tracker 4x4 is not working, it could be due to a faulty temperature sending unit, a broken gauge, or an issue with the wiring or connections. First, check the fuse related to the gauge and inspect the wiring for any visible damage. If those appear fine, consider replacing the temperature sending unit. If the problem persists, the gauge itself may need to be repaired or replaced.
1996 prelude temperature gauge reads low temp
probably the sensor
The most common reason for a 1996 Chrysler Cirrus odometer and RPM gauge to stop working is a fuse. If the fuse is removed from the dash and replaced, often times the odometer and RPM gauge will begin working.
on the side of the radiator
If the gauge isn't working, then the sending unit has failed.Easy enough replacement and doesn't cost much.See "Related Questions" below for more
Bad temperature sending unit? Bad gauge?
Check connector and wire for shorts/breaks.
Could be the coolant temperature sensor.
sending unit
age of car - although be careful that you do not have any leaks anywhere - this happened to me in a slot canyone in UT - the truck i had blew up