Temperature Gauge Calibration Question

Are you not happy using an I/R heat gun?
I'm pretty sure Palo Alto does the calibration. I know they calibrated my speedo, although it didn't stay accurate very long. I'll send it back this winter and try again.
Wire up the temp sender out of the car and put it in boiling water.

TomB

 

Honestly, the resistance involved is so small, that the wring of your car makes a difference in the calibration.

The best way to do it is buy a linear potentiometer, 0-1k (not "audio taper"), and disconnect the wire from the sender.

Place the potentiometer in line with the sending unit wire and ground the other end to the block next the sender. Jump the center terminal to one of the ends, like a guitar)

Withe car running,Turn the pot until the gauge is at the "100" mark (or 212).

Now measure the resistance of that pot. The ohms should be in the hundreds. This is what your existing or replacement sending unit should be. Try a new sending unit perhaps, but never throw away the old one.

If you need to tweak the gauge, you actually bow the arm of the back of needle so it is accurate at 100 or 212 boiling point

 

OEM instruments are generally pretty crude devices. In my opinion they represent what could be best described as an "impression" of the value they display.

Back in the 90's Jaguar had complaints about their oil pressure gauges reading low at idle (a normal condition). The "fix" was a kit that made the gauge read mid-scale any time the pressure was more than about 2 pounds.

 

my understanding is that the grounds will affect the gauge reading.

Have you located the ground for this circuit?