does anyone know the factory water temperature sender ohm value for a mid 70's big block ? i tried to search, but failed in finding a result.
as usual, TIA !

See pic

I'm under the impression that those senders generate a small amount of current, voltage, not increase or decrease the Ohms

Voltage variation is due the ohms variation

It's a variable resistance similar to a fuel gauge sender.

I know the fuel sender is a varistor (variable resistor) but I've been told that both the water temp and oil pressure senders generate current back to the meter, not resistance
I'll have to do some testing on the water temp senders I have in both hot and then cold water using a good VOM using Ohms and then very low DC voltage

The fuel sender would technically be called a rheostat (variable resistor).

A varistor is a different device where the resistance varies with applied voltage. A lighting arrestor many times is a varistor. A rheostat is a variable resistor with 2 connections and a potentiometer is a variable resistor with 3 connections.

If I understand it correctly, there is a resistance value of the sender that varies with the temperature (or pressure for oil). The system is set up to supply a small (5 volts) to the circuit. The voltage at the return of the circuit is measured by the gauge. The gauge is indicating how much current made it through the circuit. The higher the resistance, the less current that made it through the loop, the lower the reading on the gauge. The lower the resistance, the more current that makes it to the gauge, and the higher the reading. Note on the photo, the reading at low temperature is highest resistance and vice versa.

Of course, I am a mechanical engineer, and my rudimentary understanding of most electrical stuff is that once you let the smoke out, the device doesn't work.

stuffing the "secret smoke" back into the wire is a pretty tough thing to accomplish ! [i've tried it with not much success ]

the 74/23/10 value i am familiar with for the gas gauge, but i thought the oil and water senders were different ? i also know the light senders are different than the gauge senders.

the reason i am asking, is i have a bunch of different temperature senders, and the sure "look" like they could be for a chrysler engine, but i don't know how to test them because i don't have the factory sending unit tester tool. so ????????

" Connect one load of C-3826."
From the pic in the second post, is this a typo?
Should it not be connect one lead?

And a thermistor varies with heat. Like the ballast or the choke regulating resistor on later Mopars. Or the temperature sender.

https://www.forabodiesonly.com/mopar/threads/engine-temp-sensor-specs.184924

I would not think that a thermistor would be used for a temp sensor in a car. A thermistor is a very non-linear device and I don't believe that would be well suited for this application. I believe a linear device like a RTD would be more suitable for a temp sensor, but I do not know the exact technology used in the temp sensors.

thanks for the A bodies link. interesting reading.

https://en.wikipedia.org/wiki/Thermistor

read list of uses for NTC type

It's a NTC Negative Temperature Coefficient resistor. It does not produce voltage. As temperature goes up resistance goes down. It is the second resistor in a series circuit. The first resistor is mounted in the gauge and is fixed. As resistance in the temp sender changes with temperature the current in the circuit changes thus changing the magnetic field in the first resistor (gauge). The magnetic field acts on the metallic needle and moves the needle.

OK, technically it's a parallel circuit. The first branch is fixed and produces a fixed magnetic field that pulls the needle low (cold). The second branch has a fixed (apposing) resistor opposite the the first branch in the gauge and the the variable NTC down-circuit. As temperature rises, resistance lowers and current in the second branch goes up creating a stronger magnetic field and pulling the needle high (hot).

Lets simplify this...
Basically the temp gauge like the fuel gauge, oil pressure are a 5VDC meter.
The water temperature sensor varies its resistance with water temperature variations so that the meter tracks accordingly.

Just my $0.02...

all righty then ! you guys have "learned me" something new. now, if i can just retain it ! i think more and more about trying that "brain medicine in pill form" they sell on late nite TV.
so now, using the 74/23/10 chart, if i touch the negative [black] probe [of my digital ohm meter] to the base of the sending unit that is immersed in the coolant, and touch the positive [red] lead to the signal wire end of the sending unit, it should read close to 73 ohms at room temperature, correct ? my main goal in all of this, is to weed out possible generic sending units from factory chrysler sending units.
thanks guys ! you have been very patient with this old geezer !

Yes, you have it.