Could be the temp sending unit located on the driver's side head, between the #1 and # 3 spark plug.
The temp sending unit for the temp gauge is located on the drivers side of the engine between cylinders 3 and 5 spark plugs.
normally the gauge should be in the middle.(between hot and cold) that is concider operating temp.
It goes to the temp gauge which is usually screwed in the head between the manifold on the drivers side, or into the thermost housing on the intake manifold.
Hey Rick==You possibl;y knocked the wire from the sender while you were working on the thermostat. GoodluckJoe
The temp sending unit on the engine could be unplugged or faulty.
bad temp sender usually. Bad gauge rarely.
i change the thermostat and the temp switch but still not working
If your temperature gauge isn't working the problem is a bad gauge, grounded or disconnected wiring or, most likely, the temp sender isn't working.
1993 chevy 4.3 v6 1500 truck temp gauge inoperative,
probably the sensor
Check your grounding on your temp sending unit.
Because they are broken is one reason
Temp. sensor my have stopped working. Quick and fairly easy fix.
Probably the temp sending unit.
Could be temperature sensor Could be gauge
Please visit the dealer to get these problems fixed.
Likely a bad ground in the relay