1937 Tempreture gauge at rest - cold or hot????

Guys, I'm having hard time getting my temp gauge to work. I have purchased from KM a new sending unit. When no power is supplied, my gauge shows cold. When power is supplied it begins to go to the mid-range and when the engine is started, it quickly goes to hot even though the engine is cool to the touch.

Michael from KM is needing to know if other '37 Zephyrs are like mine - that is when the power is off, is your temp needle hot or cold? Mine is cold.

The way a King-Seeley gauge works is this. The gauge and sender are in series with each other. The sender has a set of points with a bi-metallic strip with a heater wire wraped around it. The gauge just has the heater wire wraped around the bi-metallic strip. When current is applied, the strip get heated by the heater coil and deflects. The pointer is attached to the strip Here's where it gets dicey. The points in the sender are controlled by pressure (oil), temp (water), and mechanical movement (fuel). These three 'inputs' control where the one contact is. The closer this one contact is to the other contact on the bi-metallic dictates how much current is flowing through the gauge thus how much deflection you are getting on the needle.

So, it makes sense that for a full tank of fuel the 'controlled' contact is closer to the heater contact, same with the oil pressure and water temperature.

BTW, I've had the gauges apart and they can be adjusted (not the ammeter) and calibrated.

John Mc My 38 LZ temp gauge reads cold with the ign. sw. off. As the engine warms up the temp gauge reads hotter. I have seen 39 Ford temp. gauges read hot when the ign. is off!!! When the ign. sw is turned on the gauge reads cold then slowly reads hotter as the engine warms up, I think this system has two senders , one in each head wired in series. These senders could be different to the single sender circuit. You may have one of those in your single sender system giving you a false reading.

38,

The two sensors used on some Fords were set up in series. The one with two terminals is a switch. On temperature rise it closes, sending gauge current to the single terminal one. I wouldn't think that John would have installed the two terminal one as he wouldn't have the wires.

To answer John's question as far as my 38 goes. Switch off it reads cold. Switch on it reads cold. TEST...with sensor disconnected, switch on, connect a test clip from the sensor terminal to ground quickly as the gauge will take off toward full hot within several seconds. It will only take several seconds for this test so REMOVE test lead quickly.

I would think someone has already PM John with this answer.

I've done a lot of talking with Michael at KM Lifestyle. I am beyond impressed with his knowledge and customer service. This stuff is really over my head but it appears that in 1939 Ford changed how the resistance is read by the gauge. Up to 1939 the gauge without power would read cold but in '39 and later the gauge goes to hot without power. I bought a new sending unit from KM and it was reading the exact opposite of what it should be, in other words when the engine is first started the gauge shows nearly full ho but as the engine warms up the needle falls towards the mid-point. So KM is sending me a new unit that is set up to read properly. Thanks to all who answered, I really appreciate it.