Technical Ford Flathead Temp Gauage Issue

1951 Ford Flathead
Temperature gauge before start up..............H (as it should)
Gauge after start up........................................C (as it should)
Gauge after warmed up engine.....................C+ plus a very little (malfunction)

Shut engine off....turn on key......temp gauge now shows proper temp.
Start engine again.............................................C+ plus a very little (malfunction)

Changed both temp sending units with known good working ones....same result as above.

Help!! Any ideas???

 

Try this: remove the wires from the temperature gauge and connect the wires from off the gas gauge and connect them to the temp gauge. Same gauge, different face. If the needle rises with the temperature, the temp gauge is bad. If it still doesn't respond, one or both of the engine units are bad or mis wired. The single terminal on the right side head is just a switch that opens when the temp rises to a harmful temperature, causing the dash gauge to go to hot as far as it can. Hope this helps.

 

If I'm remembering correctly the 2 pole unit is a switch and the single pole unit is a normal style sending unit. Otherwise your information is correct.

 

Do you have good thermostats in your engine? At my age the old memory is a little sketchy at times. I'll double check and let you know if I'm incorrect.
Glenn

 

pull the sender wire off and connect it "in-series" to ground with a cheap $2 potentiometer [and dial it up and down and watch the needle move]
While doing this you can measure across the potentiometer for resistance [ohms] with the needle in different positions.

This will give you a reference to measure resistance of the sender units at different temps.
And if there is a break in the wiring somewhere it should show up [or a faulty gauge]

 

These senders are not resistors, they are a heater that heats up a bi metallic strip which when it get hot opens a set of points, when the points open, the heater circuit is open until the bi metallic strip cools down and resets the circuit. As the water gets hotter, the circuit opens and closes faster making the gauge read higher.

 

chevyfordman: When I carefully took my temp. sending unit apart (like you did) the unit did not have that
yellow piece of paper? inserted in the unit like your photo shows.
Is that supposed to be there? If, so, what is it made of?
I have several Ford flathead temp. sending units that I would like to repair.
OEM units are now rare and expensive.
Thanks, JIM