On Sun, 27 Jan 2013 13:34:21 -0500, wrote:

Without coolant the guage will in all likelihood never go up - or the
light come on. Bothe measure COOLANT temperature, not engine
temperature. No coolant, no indication.

Yes, this is correct. The sensor goes right into the coolant. The last
time I changed a sensor, I had to drain the coolant first, or it would
have spilled all over the place.