The Ford Barn

1950 custom · 05-02-2022, 08:49 PM

I would think most here know theses flatheads have two temperature sending units. One with one terminal and the other with two terminals. I know the one with two terminals is strickly an on-off switch. The one terminal actually controls the temperature gauge by I think changing the resistance. My questions are
1. What is the temperature at which the two terminal switch closes and gives a ground to the circuit causing the gauge to move to hot?
2. At what temperature will it switch back?
3. Is there a resistance chart vs temperature for the one terminal sending unit that causes the gauge to move?

tubman · 05-02-2022, 10:05 PM

First of all, you should know that Ford gauges do not use variable resistance. They operate on the "King-Seely" principle, which uses bi-metallic actuators in the sending unit that sends different pulses to the gauge that has a corresponding bi-metallic unit in the gauge that causes the gauge to register the reading.

A short search on the internet says the dual terminal gauge closes at 220 F. I would imagine that that it may vary between units, but it sounds about right.

1950 custom · 05-03-2022, 08:50 PM

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I will try to do some research on that. I didnt think it would be like a thermistor that changes resistance based on temperature where there is a specific resistance for each degree. I could see a resistance change in the unit but it was quickly changing.
Thanks for the information.
Do you know the normal operating temperature with 180 degree thermostat? I am guessing somewhere between 180 and 190?

05-02-2022, 08:49 PM	#1
1950 custom Junior Member Join Date: Apr 2022 Posts: 6	1950 239 flatheat water temperature sending units I would think most here know theses flatheads have two temperature sending units. One with one terminal and the other with two terminals. I know the one with two terminals is strickly an on-off switch. The one terminal actually controls the temperature gauge by I think changing the resistance. My questions are 1. What is the temperature at which the two terminal switch closes and gives a ground to the circuit causing the gauge to move to hot? 2. At what temperature will it switch back? 3. Is there a resistance chart vs temperature for the one terminal sending unit that causes the gauge to move?

05-02-2022, 10:05 PM	#2
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 10,317	Re: 1950 239 flatheat water temperature sending units First of all, you should know that Ford gauges do not use variable resistance. They operate on the "King-Seely" principle, which uses bi-metallic actuators in the sending unit that sends different pulses to the gauge that has a corresponding bi-metallic unit in the gauge that causes the gauge to register the reading. A short search on the internet says the dual terminal gauge closes at 220 F. I would imagine that that it may vary between units, but it sounds about right.

05-03-2022, 08:50 PM	#3
1950 custom Junior Member Join Date: Apr 2022 Posts: 6	Re: 1950 239 flatheat water temperature sending units Sponsored Links (Register now to hide all advertisements) I will try to do some research on that. I didnt think it would be like a thermistor that changes resistance based on temperature where there is a specific resistance for each degree. I could see a resistance change in the unit but it was quickly changing. Thanks for the information. Do you know the normal operating temperature with 180 degree thermostat? I am guessing somewhere between 180 and 190?