Water Temperature guage not working

Disconnect the wire from the temperature gauge sending unit and ground it. That is, connect it to something metal that's not painted. Turn the ignition on. The temperature gauge should swing to hot. If it does, the sending unit is bad. When you replace it, don't put any sealant on the threads! If the gauge doesn't swing to hot either the gauge itself is bad or the wiring going to it is bad. One other remote possibility is the thermostat is stuck open and not allowing the engine to warm up. This is a suspect if you have no heat as well as the gauge not moving. Hope that helps! Jim