While 80 or more ohms = no needle movement in the gauge, a temp sender can go a long way beyond that and still be good. Oil and temp senders don't have fixed limits like fuel senders.
Buy one anyway. They don't cost much.
Right, the temp gauge sender readings can go to many thousands of ohms when fully cold; some of the newer ones seem to reach a 'break point' when cooling down where the resistance goes essentially 'open' (very, very high resistance).
OP, after you have tested the temp sender resistance, put your meter back on the 20V scale, connect the black lead to the temp sender case or alternator case (a good ground on the engine), and connect the red lead to the wire for the temp sender while it is disconnected from the temp sender. Turn the key to RUN and see if the voltage is jumping up and down between very low and as much as 12V.
If the sender resistance is as low as the 1.2 ohms that you measured, it may have burned out the Voltage Limiter or the gauge as Pete mentioned. Since the fuel guage does nothing with the fuel sender wire groudned, I would susepct the Limiter first. So both tests are needed.
