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Old 09-04-2019, 10:32 AM   #1
AndrewNance
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Default 140 temp gauge wonky

The water temp gauge in my Ď71 is acting pretty strange. Immediately after starting it will start climbing and go all the way to the red. While driving it fluctuates pretty rapidly, or at least more rapidly than temperature actually fluctuates. The sender in the head is new. Do these gauges ever really go bad? Maybe a bad sender?
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Old 09-04-2019, 10:49 AM   #2
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Fuel reading low?
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Old 09-04-2019, 10:50 AM   #3
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There's a voltage reducer/regulator that supplies lower voltage to the gauges. When cold, it briefly supplies full 12V, so the gauges 'jump', then a thermal switch opens and it gets reduced current via a resistor (I think the same wire wrap that warms the thermal switch).

That can and do go bad. Commonly failing to open, which keeps 12V flowing to the gauges, which peg out and burn out eventually.

https://www.sw-em.com/voltage_stabilizer.htm


This would affect fuel and temp gauges though, so on second thought, probably not that.

Look for issues with the wiring between the sensor and instrument cluster?
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Old 09-04-2019, 11:03 AM   #4
AndrewNance
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Fuel gauge is reading normal. The temp gauge does just sit all the way to the right most of the time.
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Old 09-04-2019, 11:07 AM   #5
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Originally Posted by Redwood Chair View Post
Fuel reading low?
Mine does.
Why?
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Old 09-04-2019, 11:51 AM   #6
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Quote:
Originally Posted by AndrewNance View Post
Fuel gauge is reading normal. The temp gauge does just sit all the way to the right most of the time.
A common problem with the stock temp and fuel gauges are loose connections.

The 2 gauges are attached to the PC board with brass nuts. These are also the paths of contact for the gauges and the nuts can become loose. If left loose long enough some corrosion can also form and a simple cleaning of the contacts on the PC board might also be necessary.
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Old 09-04-2019, 11:59 AM   #7
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Right on. I’ll give it a look. For what it’s worth, it all worked just fine before the car spent a considerable amount of time sitting.
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Old 09-04-2019, 05:36 PM   #8
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Quote:
Originally Posted by AndrewNance View Post
The sender in the head is new...Maybe a bad sender?
My first guess was sender. New doesn't always mean good.

Any chance you have a spare to swap in?
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Old 09-06-2019, 10:15 AM   #9
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Originally Posted by alschnertz View Post
My first guess was sender. New doesn't always mean good.

Any chance you have a spare to swap in?
I donít believe I do. Need to check the back of the cluster and see whatís happening back there.
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Old 09-06-2019, 12:35 PM   #10
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New now a days means, never ever works
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Old 09-07-2019, 08:07 AM   #11
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Quote:
Originally Posted by AndrewNance View Post
I donít believe I do. Need to check the back of the cluster and see whatís happening back there.
If you are going to be experimenting / troubleshooting the gauge, be aware that if you apply 12-volts to it, you'll kill it.

I believe the voltage stabilizer's output is only 5+/- volts.
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Old 09-07-2019, 11:50 AM   #12
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Originally Posted by alschnertz View Post
If you are going to be experimenting / troubleshooting the gauge, be aware that if you apply 12-volts to it, you'll kill it.

I believe the voltage stabilizer's output is only 5+/- volts.
Good to know! Iím hoping to find a GT cluster for this car so I wonít go too deep into troubleshooting. I can toss in an aftermarket temp gauge if I need to.
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Old 09-09-2019, 09:19 AM   #13
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AFAIK the 140 GT cluster uses a voltage 'stabilizer' as well.
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