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I have looked everywhere, Autozone, OReillys, Pep Boys, etc. and I cannot find a water temperature sending unit for the temperature gauge on my '80.

I HAVE found several but they aren't compatible with the Chevy gauge. Using a variable resistor in place of the sending unit, I measured that the gauge needs about 100 ohms to read 220 degrees and about 300 ohms to read 100 degrees (+/- something).

All the senders I found are pretty close on the 100 degree end (323-390) but far off (24-42) on the 220 degrees end.

Does anybody know where I can find a true replacement unit?

Jack
 

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I have looked everywhere, Autozone, OReillys, Pep Boys, etc. and I cannot find a water temperature sending unit for the temperature gauge on my '80.

I HAVE found several but they aren't compatible with the Chevy gauge. Using a variable resistor in place of the sending unit, I measured that the gauge needs about 100 ohms to read 220 degrees and about 300 ohms to read 100 degrees (+/- something).

All the senders I found are pretty close on the 100 degree end (323-390) but far off (24-42) on the 220 degrees end.

Does anybody know where I can find a true replacement unit?

Jack
www.rockauto.com Look in Electrical - Switch & Relay, then Temperature Switch. There are several choices of gauge senders there.
 

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i have the auto zone one in my 86 and it reads correct you may have got a bad one .try napa they are spendy but usually good.when i was in ca last week i had to repair the dash on my budys 85 the gauges quit. found that the printed circuit broke the hot strip before the first gauge. a quick solder job and was good.while in there i soldered all of the gauge clips to the circuit board and his temp and volt meter started reading real close to actual ,he was complaining of them being off before they quit. might want to check your
 

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Jack_K, those resistance measurements you mentioned appear to be lower than the GM specs. The actual GM spec is 1365 ohms at 100 deg F and 55 ohms at 260 deg F. At 212 deg F or so, (in boiling water), I've measured four sensors to read 180, 160, 190 and 180 ohms. At 105 deg F, they measured 1415, 1445, 1525 and 1590 ohms. The 1983 ECM temp sensor spec is 1600 ohms @ 100 deg F, 450 ohms at 160 degs, and 185 ohms at 210 deg F; the 1989 ECM temp sensor spec is the same. I'm not sure whether you can substitute an ECM temp sensor for the gages but in any case, the ECM sensors have either a coaxial connector or a 2-prong connector whereas the gage sensor has a single tab. The graph below was created ten+ years ago. A series of measurements of coolant sensor resistance versus temperature were taken by immersing the bulb end of the sensor in a pan of heated water. The water temperature was measured using a wide-range digital thermometer kindly furnished by Dave Worthington with a specified accuracy of +/- 2 degrees Fahrenheit. Resistance was measured with a Fluke digital Volt-Ohmmeter with a specified accuracy of better than 1%. Sensors (including the thermometer) were placed into a hole punched into a sheet of kitchen aluminum foil which partially-covered the pan of heated water. The water was heated over a gas stove and stirred within the pan with a turkey baster syringe until both the temperature and indicated sensor resistance had stabilized to better than +/- 0.2 degrees F and 2 ohms for at least 10 seconds. Measurements were then recorded.

 

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Jack_K, those resistance measurements you mentioned appear to be lower than the GM specs. The actual GM spec is 1365 ohms at 100 deg F and 55 ohms at 260 deg F. At 212 deg F or so, (in boiling water), I've measured four sensors to read 180, 160, 190 and 180 ohms. At 105 deg F, they measured 1415, 1445, 1525 and 1590 ohms. http://i713.photobucket.com/albums/ww137/SteveH057/GM Temperature Senders/TempSe1.gif
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.

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.

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?

When did you get the GM spec on the sensors?

Jack
 

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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.
 
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