[Formulabruce]

I agree with transamric, however, we need to look at a couple things
1. Steve that link to article is for a small block Corvette, look at the picture at the bottom with the teflon tape mythbuster!!
3. That said, the resistance in the GM sending units for guages was made to work where there was alot of heat sink, IE water around it in the top of the intake. I ran a 71 with guages and it always seemed hot, tried new senders, even letric, and similar results, then I moved the sender to the the intake for yuks, and put an infrared gun on it and bam it worked well, and correct'
4. These units for switching on an idiot light from the head, or turning on fans in newer cars work fine and head temp ALWAYS leads engine temp, unless ya own a 3rd gen LT-1. That said, I have never been able to nail down the guages correctly even with new GM sensors way back in 78 when my neighbor brought his pontiac over.
5. Conclusion, the senders from letric work perfect for 70-73 cars factory guages if you put the sender in the intake, by the thermostat, ( spark unit location on some)
I looked for a spec on the actual debth for the sensors of=r the actual length of them, and actually used a small extender in the head once, which I thought would be good but it heats up and no way to cool the metal, not enough water. Finally I firmly believe that GM had in mind using these in the intake for readings, look at their design, they are so close to hot metal near only 2 cylinder in a head .
If you get a sender for guages to read that your engine is at 180, and the sender is in the head, your probably running at a dynamic ( t stat open) temp of 160 . The thermostat is designed to control engine temp, makes logical sense to read the temp there.. I battled this on non chevy,GMC stuff for a bunch of years
PS not trying to stomp on any toes here....