Unless you can find a spec somewhere for 35 deg there is no way to know. And if somehow you figure the sensor is OK (or replace it with a unknown Asian one) that still leaves the question as to whether the gauge is OK or there is some resistance somewhere in the circuit that's being read as sensor resistance.
That's why , were it me, I would test the whole system as a system as I described earlier.

 

After searching, I found these two charts. I think that the first one is for the sensor that goes to the computer, and the second is for the gauges. I don't know what years they are for, but I assume they are all the same. Based on the graph, the sensor that feeds the computer is good and I'm getting up to temp. I have not tested the other one yet since I didn't even know it existed until an hour ago.

 

After some research, I think the last picture is the coolant temp sensor for the computer's resistance for Renix XJs. I found this:
Temperature Gauge Calibration
Pointer Position ...............Resistance
100°F Graduation(±3.5°) ...1365 ohms
220°F Graduation(±2.5°) ....93.5 ohms
260°F Graduation(±2.5°) ....55.1 ohms

I think it's for the gauge temp sensor for my year xj.
Using what I learned in calculus if I did it properly, 160F should be 500 ohms, 180 should be 320 ohms, and 212 should be 124 ohms. If anyone is interested, here is the equation: 0.06022x^2-29.87x+3750.

EDIT: So my math was wrong, and I cant figure out how to do it correctly, but I did find this websitehttps://www.thinksrs.com/downloads/p...alculator.html

where I can put the temp and resistance values, and it seems correct.

 

I'll throw this piece of data into this insanity.
my 2000 (note it has a nice new brass heater core and 2000's don't have heater valve so coolant circulates thru core all the time once warm enough- so a bit of extra cooling there.
Anyway this morning xj had been parked in 25 degrees garage all night. Outside at house was 12 degrees.
drove 2 miles/10 min to bottom of hill where it was 3 degrees. At that point gauge was about 1 needle width below 210 (where it usually lives) and I had reasonable heat (once things get stable that heater core will run me out of there)
At some point you need to bite the bullet and go to Wally World ,spend $3 on a thermometer that goes to 212 so you can figure out what's going on.

 

where do you buy the mopar thermostat? What’s the next best thing if it’s not available?

 

Jeep dealer. Mopar online parts sites.

 

I think I solved the problem! I tested the gauge and wiring with some resistors, and it worked fine. The resistance that the other coolant temp sensor shows that the jeep was heating up fine. So the culprit should be the coolant temp sensor that feeds the gauge. I will replace it.

 

I solved the problem by replacing that sensor.

 

Nice.