Need a bit of information on temp gauges. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

HO455 · 03-27-2025, 08:35 PM

Should the factory temperature guage needle drop to cold when I turn the key to off? Or does it slowly drift down like the fuel guage?

I had a weird ignition switch anomaly a month ago where when I turned the key off the engine stayed running. I had to disconnect the power to the coil to get it to shut off. Then after poking around under dash I restarted the engine and it shut down normally and has ever since. But I have noticed that the temperature guage doesn’t drop when the ignition switch is switched off and for some reason I think it should.
Thanks for any help.

RustyPile · 03-28-2025, 07:27 AM

There is no common solution to every electrical problem.. A step-by-step diagnostic procedure is required to arrive at the problem.. That continuing to run issue will be back.

There is no "assigned position" for the needle of a temperature gauge after the power is removed from it.. Each gauge will seek it's own "comfortable position.. Same thing applies to a fuel gauge.. Both gauges basically operate the same.. A voltage is applied to the gauge(s).. The ground path for the gauge winding is through a variable resistor.

In the case of the temperature gauge that resistance varies according to the amount of heat applied to the sensor..

In the case of the fuel gauge, A float moves the wiper of a potentiometer in order to vary the resistance..

HO455 · 03-28-2025, 08:40 AM

Thanks for the information. I've been waiting for the other shoe to drop on the ignition switch.

The battery in the truck went dead after I parked it for 5 days (due to a bad head gasket.) I think that I may have some parasitic drain on the system, maybe related to the switch. In my mind was thinking the guage was still powered up when the switch was in the off position.

Or it could be that my 2019 vintage battery is no longer up to the task but it did stay charged on the bench for the week it took to replace the head gaskets. Unfortunately time has been in short supply as of late and that's what it's going to take to get to the bottom of this.

Thanks again for making one less rabbit hole for me to dive down.

Casper42 · 04-03-2025, 09:06 PM

No - temp gauge stays where it was last in the ignition "on" position. Next time you start it, it will drop back to cold.

03-27-2025, 08:35 PM	#1
HO455 Registered User Join Date: Feb 2016 Location: Portland Oregon Posts: 12,411	Need a bit of information on temp gauges. Should the factory temperature guage needle drop to cold when I turn the key to off? Or does it slowly drift down like the fuel guage? I had a weird ignition switch anomaly a month ago where when I turned the key off the engine stayed running. I had to disconnect the power to the coil to get it to shut off. Then after poking around under dash I restarted the engine and it shut down normally and has ever since. But I have noticed that the temperature guage doesn’t drop when the ignition switch is switched off and for some reason I think it should. Thanks for any help. __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

03-28-2025, 07:27 AM	#2
RustyPile Registered User Join Date: Dec 2017 Location: Elkhart, Texas Posts: 2,108	Re: Need a bit of information on temp gauges. There is no common solution to every electrical problem.. A step-by-step diagnostic procedure is required to arrive at the problem.. That continuing to run issue will be back. There is no "assigned position" for the needle of a temperature gauge after the power is removed from it.. Each gauge will seek it's own "comfortable position.. Same thing applies to a fuel gauge.. Both gauges basically operate the same.. A voltage is applied to the gauge(s).. The ground path for the gauge winding is through a variable resistor. In the case of the temperature gauge that resistance varies according to the amount of heat applied to the sensor.. In the case of the fuel gauge, A float moves the wiper of a potentiometer in order to vary the resistance..

03-28-2025, 08:40 AM	#3
HO455 Registered User Join Date: Feb 2016 Location: Portland Oregon Posts: 12,411	Re: Need a bit of information on temp gauges. Thanks for the information. I've been waiting for the other shoe to drop on the ignition switch. The battery in the truck went dead after I parked it for 5 days (due to a bad head gasket.) I think that I may have some parasitic drain on the system, maybe related to the switch. In my mind was thinking the guage was still powered up when the switch was in the off position. Or it could be that my 2019 vintage battery is no longer up to the task but it did stay charged on the bench for the week it took to replace the head gaskets. Unfortunately time has been in short supply as of late and that's what it's going to take to get to the bottom of this. Thanks again for making one less rabbit hole for me to dive down. __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

04-03-2025, 09:06 PM	#4
Casper42 Registered User Join Date: Nov 2022 Location: Seattle, WA Posts: 612	Re: Need a bit of information on temp gauges. No - temp gauge stays where it was last in the ignition "on" position. Next time you start it, it will drop back to cold. __________________ '72 C10 Cheyenne SWB North Carolina kept for 50 years, 75k original miles, Medium/Hawaiian Blue paint, 3 owners - one for 40 years & garaged kept. Original: sheetmetal, undercarriage, moldings, glass, immaculate unrestored bed. * * * New - rebuilt engine at 65k in 2015, one frame-on respray in 2010, front bumper, blue houndstooth seat, carpet, 8 inch rally wheels on 275-60R-15, LED lighting. - Semper Paratus!



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