70 Challenger 440: Temp gauge doesn't move. When pulling the wire from the sensor and grounding it the gauge goes to hot as it should. Put a ohm meter on the sensor and resistanse starts to drop as soon as I grab it and raises again when letting go. Tried the same, and got the same result on another old sensor I have. None of them makes the gauge move when mounted and taken for a 10 min. test drive. The ohm meter shows a little different between the when cold - one reads 1.2, the other 0.95. Can they both be bad or am I overlooking something?

All the Chryslers I've ever dealt with if the gauge moves when grounded, the gauge and circuit are good, the sender, not so...

run a jumper from the sender body (not the threaded stud) to a good ground & plug in the L female connector & run it & see if it starts to come up on the gauge.

Yes the sender needs to be grounded. I had teflon tape on one and it wouldn`t work.

I would put the sender in a pan of water on a stove and heat the water up while you watch the senders ohm reading

There's your answer, has to be the sensor or how it's mounted.
The sensor is a variable path to ground dependent on temperature.
No path, gauge doesn't work.

also, don't overlook any corrosion or deposits on the bulb portion that is in the water flow path. those deposits can insulate the sender and make for low[er] temperatures. cleaning the bulb to shiny brass can sometimes bring your sender back to life. i have done this many times over the years, and saved quite a few senders that would have been replaced. no guarantee, but you have nothing to lose other than a few minutes. and definitely no teflon tape on the threads to cause a grounding issue.

Great, guys! No teflon tape, but thread sealer. Is that a big no too? I haven't had trouble with that earlier. I'll ground the sender upon next drive and see how it does.Don't think deposits or corrotion is the problem as they look shiny and clean. Does anyone know what ohm readings a good sender will put out hot ans cold?

I can get you a cold reading from one on the bench later on today.

I'm getting around 250 ohms cold (75 room temp)

Thanks for the reading! All mine measure way higher. I red somewhere that they should be in the 2k area when cold. Don't know if that is right. Ohm'd the two sensors again in room temp. One is around 900, the other 1200. Found a third one I forgot I had. It looks unused and measures 1700. All three starts to fall when warmed between the fingers. Threw the third one in but I am fighting a leaking trans pan so I won't be able to test it in a couple of days. Robert: Do you too have a good one you could measure?

My one I had loose is showing open, I will see if I can grab another one. What I would do now is get it hot in your driveway (or go for a ride then come home) & clamp a jumper cable around the sender body & the other end of that cable to the batt neg post & see if it reads. That way you ain't gotta undo anything to see if it is a ground contact issue. it for sure is gonna have less than 2K ohms.

Why don't you install the sensor, warm the engine up, and then check the sensor resistance? The FSM uses the same tester (C-3826) for both the fuel gauge and the temperature gauge so the resistance ranges should be similar.

Thanks! Haven't got the car out for another test. Third sender is in and we'll se how it does. Sure could read them warm but it would be nice to know what a good sende should read both cold and warm. Easier than swapping them in and out to find one that actually works. Maybe all three are bad. At least they all read different when cold.

That's a good thought BUT...what is "cold"? 75 degrees, 100 degrees, 120 degrees? I think the assumption that ambient temperature is the "cold" temperature in the design gauge temperature range may not be accurate. Likewise, what temperature would "warm" be? That's why I depend on the tester resistances to determine the status of a sensor.

I think if you think about the guage range, middle travel of the needle would be normal engine temp. So heat the sender to say 160* and it should ohm about 24.

Thanks both. Cold, lets say normal summer temp, but one could squeeze the sender between the fingers and read it then. Still should not move the gauge much. Warm is warmed up enging, like 180F. Don't have to be picky about the temps. I am only looking for what range readings a good sender put out. I have now tested three senders in the car and none moves the gauge. But also they all read between 800 an 1600 ohms at body temps. Went out and measured a goo working sender in the Charger and it only red 250 ohms "cold". This atleast tells me the other senders I have have far too much resistanse. Just ordered a new sender so hopefully it will be ok:)