Temperature Sender Questions

[Gary AAR]

I have recently got my 70 Cuda with stock 340 engine running, and have noticed the engine temperature gauge doesn't come off a "Cold" reading even though the engine has been brought up to operating temperature.  I grounded the sender wire to the gauge directly to negative battery terminal, and the gauge sweeps smoothly all the way to "Hot".  From this I assume the gauge and the wire from the sender to the temp gauge are good.  I then measured a resistance of 550 ohms between the temperature sending unit and ground with a cold engine.  This seemed to be way too much resistance.  I also measured the resistance of an old temperature sending unit (not in an engine) when at room temperature, and it measured about 195 ohms.

I then tried the following diagnostic procedure:
1.  I took an old fuel sender unit (out of the tank), and hooked it up to the temp sender wire feeding the temp gauge.
2.  With the fuel sender unit arm at the empty position, I had approximately 73 ohms resistance, and the temp gauge read near the "Cold" position.  With the fuel sender arm near the mid position, I measured approximately 25 ohms resistance, and the temp gauge read near a normal operating temperature position (slightly under half way between Cold and Hot).  Finally with the fuel sender arm in the full position, I measured approximately 10 ohms resistance, and the temp gauge read at the "Hot" position.

From the above procedure, can I assume I have a bad temperature sending unit?  Anybody ever tried the above procedure?  Is the resistance range of the temperature sending unit the same as the fuel sending unit (10 ohms, 23 ohms, 73 ohms)?  If I need a new temperature sender, can anyone recommend a source for a quality part?
Thanks for the help.

[DeathProofCuda]

It's been awhile since I've messed around much with gauges, but I "thought" that the resistance ranges for all of the gauges were the same (generally from around 80 ohms at the low end of the gauge and 10 ohms at the high end).  However, I just checked my temp sending unit and I got around 190 ohms between the tip connection and my negative battery cable with the engine dead cold (probably 80 degrees right now).  Unfortunately, car is currently apart again, so I can't help with a "hot" resistance number, but it sure sounds like you're on the right track.

[dodj]

Temp sender I believe is 10ohms to 80ohms. Give or take.
Put it in boiling water,  should get about 10. If you don't,  replace it.

[Jay Bee]

Check out this thread....

https://forum.e-bodies.org/electrical-and-audio/11/temp-sender/22656/

PS - water boils at 212*F