Thanks. I also used a Fluke DVM. I connected a potentiometer in place of the sensor and varied its resistance to set the gauge at 100, 220, and 260 degrees. The resistances I read were (approximate since it's a single turn pot) 600 ohms, 95-100 ohms, and 40 ohms.
I did this on two different gauges.
That's really not a good idea unless you're using a pot that can handle a couple hundred mils at the expected resistance. All 4 gages draw about 0.75 amps (Cutlass gage clusters take a bit more at about 0.85 amps), meaning just one could draw as much as 200 mils or so, which could burn up your pot unless it's a high-power type. If you apply a steady voltage to the gage center, and full 13.7V to the top and bottom, you will note that it takes around 5 minutes for them to stabilize (the needles will slowly shift about a needle's width). After 5 mins, the gages are also noticeably warmer.
I haven't done this, but think that if you have a stable adjustable power supply, you could measure the voltage applied to move the needle where you want then also the current, then calculate the resistance using Ohm's Law. To protect the gage from catastrophy, put a current-limiting resistor in series with the center connection or use a current-limited power supply (say, 100 mils or so, until you see what's happening).
Then I got smart and measured the one on the cluster that will eventually go in my car. It read 65 ohms at 260 degrees, 105 ohms at 220 degrees, and about 1300 ohms at 100 degrees.
That's about right.
What should the sensor read at about 80 degrees? All the ones I measured at the parts houses measured about 2.4 K at room temperature. I assume that's too high?
Other than for the ECM temp sensor, GM did not define what the gage sensor resistance should be below 100 degs, so I don't know for sure. But 2.4K would be within the rhelm of likelihood. I wouldn't worry about it below 100 degs since the gage doesn't really read below that temp.
When did you get the GM spec on the sensors?
It's marked on the foldout schematics in the '79 Elky Electrical Troubleshooting Manual, but I got the info for the ECM sensors from the emissions books. IIRC, the chassis service manual (at least my '79 book) states the sensor resistance, too.
I had a whole web page dedicated to these measurements as well as others but my ISP went out of bizness and after a couple years, the page disappeared. I do have it backed up here at home but not reposted anywhere yet. That's where I got today's info. I can e-mail/send you the htm file if you want, as well as the chart in gif format. Put in the same subdirectory, the page with chart should then show up.
IIRC, I also have another web page that compares gages against one another. They're all slightly different, of course. I'd have to hunt for it and it might only be for Cutlass clusters, I don't remember for sure.
