Run a test. With the ignition switch off, the temp gauge should read full hot. If not, the gauge needs repair or replace. Turn the ignition switch on; if the engine is cold, the temp needle should move slowly to cold. If not disconnect the wire at the single pole sensor and hold it to ground; the temp needle should move slowly to cold. If not, short the connection between the two poles on the double pole sensor (generally the one on the driver side). If that gets the needle to move the double pole sensor is bad and can be bypassed (connecto both wires to the same/either post) or replaced. If it still does not come off of full hot, put an ohmmeter between the single post sensor post and ground; If it reads open circuit, that sensor is bad; if it is not open circuit, check the continuity of the wire between cylinder heads and the wire from the driver side sensor to the temp gauge under the dash. To do that ground the end of the wire at the engine driver side, and then check the other end of that wire at the gauge with an ohmmeter; should read near zero ohms; if open circuit, the wire is bad (rare). If the wires are good, it may be the gauge or lack of power to the gauge. Disconnect the wire at the driver side sensor to create and open circuit there. With the ignition on, you should have 6 volts at both terminals on the back of the temp gauge. If you have 6 volts at only one terminal the gauge has gone open circuit/bad. If you do not have volts at either terminal something has come disconnected or broken between the gauge and the ignition switch terminal. Some instrument arrangements have power to two gauges jumpered together with a short strip. Check that too.
Good luck. You are going to need that temp gauge!
