The concept for the guage is fairly simple. in theory one side of the meter has +12v(it could be less) the voltage goes through the coil in the meter and comesout the other side. that side is connected to the wire that goes to the coolant sensor (usually on the intake manifold) the coolant sensor is a variable resistor that changes with temperature. It provides a varied level of ground potential from the intake manifold. that all said ...you can check your guage by grounding the wire for a short amount of time and seeing if the guage goes to full hot. If it does the sensor is bad. If it does not the guage is bad.
The temp gauge sensor for your engine is located down front on the engine block near the thermostat housing & hose. I would first check visually to see if the wires to this sensor are in good shape, and connected. If they look good I would as standard practice replace this sensor. The sensor is not costly, and even if not completely bad replacement should end uncertainty when further diagnosis is required. Incidentally once you find the sensor you may check the circuit by temporarily shorting the leads of the sensor ;while having a helper watch the gauge for movement. Make sure that you have the proper sensor first though. The sensor for the motor that you had listed does not have +12 Volts supplied to it. The temp sensor have +5V DC that is supplied to the other sensors as a source voltage.
If you have any other problems e-mail me as to what you have found.