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73-87 Chevy _ GMC Trucks => Interior & Equipment => Instrumentation => Topic started by: uprising on February 21, 2019, 02:37:46 am

Title: Temperature Gauge
Post by: uprising on February 21, 2019, 02:37:46 am

Hi guys,

i have a big problem with my original temp gauge.
1. Does the gauge need a calibration?
2. Does somebody have a pin description? Where is the sensor connected?

I have following problem:
my preowner installed a different temp gauge but i would like to use the original. Now i check the gauge at work and the result is crazy...
I set 10V on the left pin and use a resistance decade with 5k on ground. If i hit the right pin the needle goes to „h“ but don‘t fall back to C. It stays at „middle“. If i hit the upper pin it will fall back to „c“. Is this reaction normal??? Is there no spring inside the gauge to go back to „C“?
And where is the thermistor connected at the dash??

Title: Re: Temperature Gauge
Post by: Irish_Alley on February 21, 2019, 07:22:10 am

this should have all the info you require.

http://forum.73-87chevytrucks.com/smforum/index.php?board=59.0

Title: Re: Temperature Gauge
Post by: uprising on February 22, 2019, 02:05:54 am

Wow, that looks pretty good! Thanks!!

But there is still one question :)

Does the needle have a spring inside? If not, how does the needle come back to c after the ignition is switched off?!

Title: Re: Temperature Gauge
Post by: Irish_Alley on February 22, 2019, 06:58:28 am

not sure never had the urge to take one apart

Title: Re: Temperature Gauge
Post by: uprising on February 22, 2019, 07:08:12 am

Then i have to open it. Actually it makes no sense for me...
How the needle goes back to C after ignition is off >:(

Title: Re: Temperature Gauge
Post by: bd on February 22, 2019, 08:10:54 am

None of the gauges contain springs with the single exception of the speedometer.  Gauge needles rest where they do because of residual magnetism in the gauge coils and fulcrum balance of the rotating assembly against gravity.

Title: Re: Temperature Gauge
Post by: Irish_Alley on February 22, 2019, 08:40:48 am

(https://media1.tenor.com/images/17a7f11a1da0f25ea2dd0fa6fe882a8a/tenor.gif?itemid=5866727)

Title: Re: Temperature Gauge
Post by: uprising on February 27, 2019, 12:53:05 am

@Irish_Alley: thx for the link. Exactly what i‘m looking for! Sadly the pics aren‘t visible anymore...
A final question: it seems that the gauge is reacting kind of crazy. Can i easily calibrate the gauge again? E.g. Set tjhe mentioned Ohm for „cold“ and move the needle manually to the defined point?

Title: Re: Temperature Gauge
Post by: Irish_Alley on February 27, 2019, 03:25:13 am

what pics?

Title: Re: Temperature Gauge
Post by: uprising on February 27, 2019, 03:59:11 am

http://forum.73-87chevytrucks.com/smforum/index.php?topic=25339.0

Title: Re: Temperature Gauge
Post by: bd on February 27, 2019, 09:32:12 pm

Try it now.

Title: Re: Temperature Gauge
Post by: bd on February 28, 2019, 09:31:56 am

Quote from: uprising on February 28, 2019, 12:41:46 am

How is the calibration of the temp gauge working?
The special ohm and move the needle to the recommended position? I still don‘t get the exact function. If the engine temp is normal (190-200 degrees) and I switch off the ignition how is the needle comes back to cold? To drop to cold 380 ohms are needed, right? How does this happen while ignition is off?

Temperature gauge parameters were altered slightly in 1974.  So the precise resistance to cause the temp gauge needle to register correctly is different between pre-1974 and post-1973 gauges.  In a correctly functioning circuit with the ignition switch ON, a 350 Ω sender resistance will cause the temp gauge needle to point to COLD.  Approximately 70 Ω will cause the needle to point mid-scale.  Approximately 50 Ω will cause the needle to point to HOT.  When the ignition switch is OFF, the gauge needle will drift to an arbitrary rest position that is unique to each gauge.  The GM electric gauges used in the 1967-1987 truck body styles do not return to zero.  If a GM temperature gauge needle returns to COLD with the ignition OFF, it is totally coincidental.