Temp gauge accuracy
Thread Starter
Intermediate
Joined: Jan 2019
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Temp gauge accuracy
How accurate are our 40 year old temp gauges and senders?
The reason I ask it I recently installed a Dewitt’s and dual spal fans. The trigger for the fans is 195 degrees. The fans do not come on until the temp gauge shows 230ish.
I know I need to go get a digital thermometer and get the real answer, I will do that as soon as the stores open. But assuming that the spall temp sender is reading correctly, how do I fix the gauge in the car?
just got back from the store, gauge reads 230, water neck is 190, radiator was about 180 at the top and 160 at the bottom.
The reason I ask it I recently installed a Dewitt’s and dual spal fans. The trigger for the fans is 195 degrees. The fans do not come on until the temp gauge shows 230ish.
I know I need to go get a digital thermometer and get the real answer, I will do that as soon as the stores open. But assuming that the spall temp sender is reading correctly, how do I fix the gauge in the car?
just got back from the store, gauge reads 230, water neck is 190, radiator was about 180 at the top and 160 at the bottom.
Last edited by Jason 1979; Jul 21, 2019 at 11:25 AM. Reason: Addition
Drifting
Joined: Nov 2013
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From: Loud, Raw and Dangerous 1968 327 4S in Southern California
Thread Starter
Intermediate
Joined: Jan 2019
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Thanks for reminding me about Willcox. So check me here, I should...
1) disconnect wire from sender.
2) connect multimeter to sender with one lead and a good ground with the other lead.
3)start the car and check resistance about every 10 degrees and make a table.
4) compare table to the resistance listed above.
if resistance is correct for the temperature I have a gauge problem. If resistance is incorrect for the temperature I have a sender problem.
Does that sound like it would work?
Drifting
Joined: Nov 2013
Posts: 1,569
Likes: 485
From: Loud, Raw and Dangerous 1968 327 4S in Southern California
Thanks for reminding me about Willcox. So check me here, I should...
1) disconnect wire from sender.
2) connect multimeter to sender with one lead and a good ground with the other lead.
3)start the car and check resistance about every 10 degrees and make a table.
4) compare table to the resistance listed above.
if resistance is correct for the temperature I have a gauge problem. If resistance is incorrect for the temperature I have a sender problem.
Does that sound like it would work?
Redvette2
Thread Starter
Intermediate
Joined: Jan 2019
Posts: 47
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That procedure worked like a charm.
Sender is reading about 20% too high ohms across the board. So the gauge should be showing cooler than the engine is. I am confused.
Water neck never went above 177 after idling for 20 or 30 minutes.
Sender is reading about 20% too high ohms across the board. So the gauge should be showing cooler than the engine is. I am confused.
Water neck never went above 177 after idling for 20 or 30 minutes.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
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From: Unreconstructed, South Carolina
AFAIK ... as coolant temp increases, gauge sender's resistance (ohms) decreases ... inverse relationship.
be clear & consistant; each time you mention sender, specify if Spal sender or gauge sender.
be clear & consistant; each time you mention sender, specify if Spal sender or gauge sender.
Thread Starter
Intermediate
Joined: Jan 2019
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The gauge consistently reads 220-230 after the car has been running for awhile.
i bought a temp gun and the car after idling for 20 minutes was showing 180ish at the water neck, 170ish top of radiator and 160ish bottom of radiator.
at 180 the sender was at 160 ohms iirc, which should be showing way cooler than 220 degrees.
Is my vette stock?? HAHA
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2020 C3 of the Year Finalist - Modified
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What year is your car? If you have a consistently high reading buy Willcoxs adjustable resistor. I t will correct the reading as long as your readings are consistent
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Drifting
Joined: Nov 2013
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From: Loud, Raw and Dangerous 1968 327 4S in Southern California
Redvette2
Last edited by Redvette2; Jul 23, 2019 at 03:38 PM. Reason: Or add a Willcox variable resistor across the meter movement!
Thread Starter
Intermediate
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I have to pull the dash apart to replace the wiper switch anyway. I think I will check resistance on the resistor on the back of the gauge. If it is reading too low, that might cause the issue.
something is causing the resistance to the gauge to be lower than what it actually is.
something is causing the resistance to the gauge to be lower than what it actually is.
Former Vendor
Joined: Aug 2006
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
If the car has a factory gauge in it, the simple solution would be to replace the stock resistor with the adjustable one on the back of the gauge. The adjustable resistors can scale the gauge to the sender.
The ohms readings in the picture posted above were taken from multiple 1979 stock original NOS gauges back when they were available from GM. We've used these charts to calibrate these gauges (for setting the needle) for over 25 years. I still have the test charts in an old file in the gauge room here. So if you are not matching up with the chart then I'd look at that but the correction is simpler by just changing the resistor. I posted the link below and I've also posted the installation video.
https://willcoxcorvette.com/corvette...resistor-77-82
The ohms readings in the picture posted above were taken from multiple 1979 stock original NOS gauges back when they were available from GM. We've used these charts to calibrate these gauges (for setting the needle) for over 25 years. I still have the test charts in an old file in the gauge room here. So if you are not matching up with the chart then I'd look at that but the correction is simpler by just changing the resistor. I posted the link below and I've also posted the installation video.
https://willcoxcorvette.com/corvette...resistor-77-82
Last edited by Willcox Corvette; Jul 22, 2019 at 06:03 PM.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,850
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15