There are two ways to check the temp gauge. First find the wire that goes to the send unit, remove the wire and ground it to bare metal. The temp gauge should go to full not. The other is to use a digital multi meter, set the multi meter in the ohm position, put one lead on the temp sending unit where the wire is and the other lead on the engine block. Note the reading. Now start the engine and watch the multi meter the ohm reading should start to go down. If it reaches 0 ohms the engine is way to hot! Good luck.