1956 Mercury Monterrey 312, temp gauge just sits on C and never moves.  It rests at H when the ignition is off, but with ignition on it rolls over to C.  If I remove the wire from the sending unit while ignition is ON it also rolls back up to H, just like if I had turned off the car.  There is only one wire attached, but two terminals on top, which is a little weird.  I get a reading of about 20ohms between the terminal and the block  (car was warmed up at the time)

The sending unit looks just like this one but not sure if it's bad or if it's the wrong one.  I'm thinking about buying that replacement, the listing says for 1956 Ford but I know the Mercs can sometimes be a bit different.  At $60 I kinda want to make sure it's the right one first. 

The one you showed is the correct one for a 56 Ford (sedan and Tbird).  I don't know if he Merc's used the same one


54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

I have a 56 Mercury Monterey, I think the gauge in your dash is fine the sending unit must be the problem mine works just like you said yours does but it does move after the engine warms up I put a new one on mine a few weeks ago and I got it from Macs and it works just fine, I'm sure the one for the Ford is the same as the one for the Mercury. I also put another electric unit on, sending unit mounted on the intake manifold just before the thermostat, they run fairly close to each other, this lets me know if both of my working

Thanks and great to meet a fellow Monterey owner!  Very good to know, I will get that one ordered and see how it works.