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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
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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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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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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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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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Old 09-20-2019, 08:19 PM   #14
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This is where I’m at. Does this seem normal? That short blue wire with the female spade connector wasn’t connected to anything. The brass nuts were all snug and relatively clean as far as 900 year old electronics go.

It looks like someone replaced the voltage stabilizer before but cut it so they could slip it under the little mounting screw. Is it supposed to mount under that screw in the long post thing behind it?


Last edited by AndrewNance; 09-20-2019 at 08:51 PM..
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Old 09-20-2019, 10:54 PM   #15
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How was the regulator mounted? Some clusters mounted the regulator in rubber so an external (blue) wire was necessary to ground the housing. Other clusters mounted the regulator to a metal post on the board that's grounded so a separate wire wasn't needed.

I see a witness mark on the regulator that looks like it was screwed to the post. If so, the blue ground wire is redundant. Just make sure the post has a good ground.

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Old 09-20-2019, 11:07 PM   #16
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It wasn’t mounted at all, just dangling when I pulled the cluster out. So that’s likely my issue I guess. It’s entirely possible that I bumped it loose while trying to change bulbs without pulling the cluster.
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Old 09-22-2019, 08:15 PM   #17
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I swapped back and forth between two clusters and two different voltage regulators and both are giving me completely dead fuel and temp gauges. I’m thinking both of my regulators are just dead as I’ve tried them each on two different pairs of gauges.

Last edited by AndrewNance; 09-22-2019 at 08:22 PM..
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Old 09-23-2019, 01:15 PM   #18
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If the regulators put out the same voltage as the newer 240 cluster. That is a ten volt regulator. You can use a 7810 three leg voltage regulator in place of the original mechanical type. Input 12v, ground, and 10v output are the three legs. https://www.amazon.com/Quickbuying-1...tronics&sr=1-6

Actually whatever voltage output they are. You can use an electronic type. The positive voltage regulators output is designated by the last two digits. So a 7810=10v, a 7805-5v, etc. TO220 type case.

Last edited by dl242gt; 09-23-2019 at 01:17 PM.. Reason: add comment
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Old 09-23-2019, 01:26 PM   #19
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It's 5.1 volts for 140/164 -'72.
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Old 09-23-2019, 01:34 PM   #20
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So you could use an LM7805. TO220 case.
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Old 09-23-2019, 01:36 PM   #21
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The original regulator also gives it a shot of 12V when first switched on, just so the gauges jump up toward their readings, without that they'll still get there, just slowly.
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Old 09-23-2019, 05:11 PM   #22
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Quote:
Originally Posted by JohnMc View Post
The original regulator also gives it a shot of 12V when first switched on, just so the gauges jump up toward their readings, without that they'll still get there, just slowly.
Are you sure about this?
Never heard or saw any documentation of that behavior in the green book.
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Old 09-23-2019, 05:46 PM   #23
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A mechanical regulator depends on the heating of the coil around the contacts to open and close. So when first turned on. The coil isn't warmed up so the contact passes the appliced voltage to the circuit. Then the coil warms quickly and starts opening and closing the contacts to regulate the voltage.

With the LM7805 it will rise slowly like in a 240 which uses an electronic regulator in the 81 and newer dash setup. Function will be fine.
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Old 09-23-2019, 07:50 PM   #24
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A mechanical regulator depends on the heating of the coil around the contacts to open and close. So when first turned on. The coil isn't warmed up so the contact passes the appliced voltage to the circuit. Then the coil warms quickly and starts opening and closing the contacts to regulate the voltage.

With the LM7805 it will rise slowly like in a 240 which uses an electronic regulator in the 81 and newer dash setup. Function will be fine.
Disclaimer - I'm no electronics genius, so take this advice however you'd like - when I had to deal with a possibly dead voltage stabilizer (not regulator!), I used a digital volt meter. It seemed to indicate that the way the original one (as pictured) works is not by changing the 12 volts to a constant 5.1 volts, but, would continuously pass 12 volts (for a very short amount of time) and then 0 volts (also for a short amount of time. In this way, it would provide an AVERAGE of 5.1 volts, but never did it seem to actually provide 5.1 volts. Because the gauges are very slow to respond to their input, you never see the change due to this on/off cycle. Because of this, the "update it to a modern regulator", which I tried, didn't end up working. The gauges didn't respond at all to a constant 5.1 volts.

Please don't hesitate to tell me I'm an idiot and that you've personally replaced the original STABILIZER with a modern REGULATOR and gotten it to work on a car that used this stabilizer.
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Old 09-23-2019, 10:03 PM   #25
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That is another good explantion of the stabilizer or regulator. If you looked at the old type on a scope. You would see a kind of saw tooth wave showing the signal you describe. The only reason a newer regulator might not work is if that version is not rated for high enough current to work for the gauges.

In the 240 cluster the early cars used a mechanical stabilizer as well. The replacement kits used to have a electronic regulator instead.

I would imagine the older gauges may require a lager regulator for higher current load. Other than that it should work. I have only used the TO220 7810 regulator for a 240 which worked fine. So I admit I haven't used one on the older cluster.
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