I received the OEM Mopar coolant temperature sensor and installed it.
I ran the car for about an hour, watched the gauge and followed with the diagnostic reader set to look at the temperature.
IT rad up after an hour to almost the highest levels and the diag meter said about 250f.
It still didn't seem too hot and I put a big fan in front of the radiator and that didn't bring it down.
The point that the sensor is installed was reading approximately 200f.
New sensor and I am still stumped. I may take it to the dealership and pay the bucks to have them figure it out.

 

Key on, engine off, sensor disconnected, use a paperclip or something across the pins in the connector, what does coolant temp have to say? Pull the paperclip, now what does coolant temp have to say?

 

Short or open test.
Sensor unplugged and key on and it goes to full scale hot.
It stays the same with a paperclip across the terminal plug, not the sensor itself.
So I'm at a loss, why.
I plug the sensor back in and it goes to cold.
Engine was not started or ran before the test.
I would have thought it would drop to cold, minimum scale with the paperclip.
I tried it a number of times, but it didn't.
I am leaning in the direction of a thermostat not opening all the way.
Temperature at the top right of the radiator is hot, not as hot as the gauge claims, but the lower hose is about 80 to 90 F.
That would seem that the coolant is flowing at its maximum rate.
I may try swapping that out today.
But I am curious about the open/closed circuit test. That didn't go as I would have thought.

 

Resistance goes down as temp goes up, so, the test yielded expected results. For best results though, using a scanner to read what PCM thinks temp is is best..... I *think* there is a chart around here somewhere of temp vs. resistance.... might be interesting to compare that to your full cold resistance reading.

Thermostat not opening all the way would account for a few of your symptoms. Wouldn't hurt to pull it, and drop it in a pan of boiling water......

 

I have ran the gamut of troubleshooting ideas and it comes down to operator error.
I Pulled the thermostat and even did a heat test on it and the last one I had in there. Both 195F and both opened all the way.
I reinstalled the previous thermostat, even though I'm sure they are both okay and that's when I think I may have installed it backwards earlier.
with it installed, spring side into the engine, it did good.
The diagnostic meter said it never went over 201F and all my readings at the thermostat housing and sensor body and water pump, were under that.
Bottom line is it ran for one hour idling most of the time, with about one minute at 2k rpm and the temperature remained at 201F and dropped to about 198F with the higher rpm.
The whole time the dash gauge never hit the halfway point.
I appreciate everyone's input and ideas.
With all the parts new, it makes it hard to condemn any of them, but putting one in backwards is a real possibility, at least with the thermostat.
Thanks!

 

Hey, it's fixed, and THAT is all that matters.