Baffled temp sending unit
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Joined: Aug 2021
Posts: 76
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From: Abu Dhabi
Baffled temp sending unit
I’m baffled, I’ve read all the posts of the C3’s temp gauge and sending unit issues and resolutions by the members. This is my story.
A 1980 small block with the temperature sending unit on the block. The unit connection broke during rebuilding the engine so; bought a new one from a reputable parts supplier. Now the temperature gauge needle moves just a tiny bit From 100 degrees when turning the ignition on, and stays there for ever.
I assume with this test and the pegged needle, the wire and the gauge are not at fault
I know that this subject had been exhausted, any help would appreciated
Regards
A 1980 small block with the temperature sending unit on the block. The unit connection broke during rebuilding the engine so; bought a new one from a reputable parts supplier. Now the temperature gauge needle moves just a tiny bit From 100 degrees when turning the ignition on, and stays there for ever.
- grounded the green wire and the needle moved to the right.
- Bought another sending unit
- The same thing happens
- Took the center console apart to check behind the new circuit
- The resistor reads 89 ohm (good)
- Washers are in place at 6 and 12 o’clock
- Checked the sending unit which gave me higher ohms on cold water and lower in hot boiling water.
I assume with this test and the pegged needle, the wire and the gauge are not at fault
I know that this subject had been exhausted, any help would appreciated
Regards
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From: New Or-leens Loo-z-anna
You probably know NOT to use teflon tape or antisieze paste on the threads of the sending unit.
On my '68 the gauge cluster metal frame must be grounded to the metal birdcage/frame....I do not kow how the grounding is done on an '80 modl.
How much voltage is supposed to be going to the Temperature gauge on your '80 model?
Sorry...that's all rookie me has to offer.
On my '68 the gauge cluster metal frame must be grounded to the metal birdcage/frame....I do not kow how the grounding is done on an '80 modl.
How much voltage is supposed to be going to the Temperature gauge on your '80 model?
Sorry...that's all rookie me has to offer.
Thread Starter
Advanced
Joined: Aug 2021
Posts: 76
Likes: 24
From: Abu Dhabi
You probably know NOT to use teflon tape or antisieze paste on the threads of the sending unit.
On my '68 the gauge cluster metal frame must be grounded to the metal birdcage/frame....I do not kow how the grounding is done on an '80 modl.
How much voltage is supposed to be going to the Temperature gauge on your '80 model?
Sorry...that's all rookie me has to offer.
On my '68 the gauge cluster metal frame must be grounded to the metal birdcage/frame....I do not kow how the grounding is done on an '80 modl.
How much voltage is supposed to be going to the Temperature gauge on your '80 model?
Sorry...that's all rookie me has to offer.
The sender sends ohms not voltage to the gauge if I’m not mistaken
the gauge pegs to the right when the wire is grounded
i might be missing something here 🥴
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Melting Slicks
Joined: Apr 2010
Posts: 2,795
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From: Canberra Australia
2025 C3 of the Year Finalist - Modified
What brand of sender did you buy.
For my 71 I found the many did not produce the correct ohms at a given temp
Here are some variations…. The WT-203Z was even better than WT203
Sender - Ohms at 212 deg
WT203 - 85
Letric Limited 06400759 - 94.6
Autozone TU5 #1 - 114.3
Autozone TU5 #2 - 110.6
Temp ohms for 71 - From Willcox
100 (38c) 220
1st mark 109
210 (99c) 79
2nd mark 65
250 (122c) 51
For my 71 I found the many did not produce the correct ohms at a given temp
Here are some variations…. The WT-203Z was even better than WT203
Sender - Ohms at 212 deg
WT203 - 85
Letric Limited 06400759 - 94.6
Autozone TU5 #1 - 114.3
Autozone TU5 #2 - 110.6
Temp ohms for 71 - From Willcox
100 (38c) 220
1st mark 109
210 (99c) 79
2nd mark 65
250 (122c) 51
Team Owner
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From: Southern Cal Ca
St. Jude Donor '22
it will get 100% pos current and a reduced by the sender neg current.
this makes needle show the amount of power it has.
I say power because you can have volts but no amps.
make sure the pos feed will light a bulb and not just show 12v on a meter.
same applies to 12v neg.
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From: Long Island
the point I want to make is the gauge is 12v
it will get 100% pos current and a reduced by the sender neg current.
this makes needle show the amount of power it has.
I say power because you can have volts but no amps.
make sure the pos feed will light a bulb and not just show 12v on a meter.
same applies to 12v neg.
it will get 100% pos current and a reduced by the sender neg current.
this makes needle show the amount of power it has.
I say power because you can have volts but no amps.
make sure the pos feed will light a bulb and not just show 12v on a meter.
same applies to 12v neg.
Thats not correct, the temp sender is a variable resistor, it varies the resistance to ground. ( the same as a fuel tank gauge. )
On the Will *** site they show a test procedure where you can substitute a variable resistor and check the gauge readings.
Check the 12volt supply to the gauge, also check that the gauges resistor is not shorted and mounted properly. Also check the ground wire to the gauge cluster.
https://youtu.be/LvW19Eu71P4
https://youtu.be/P4207sCWtUg
Last edited by BLUE1972; Dec 25, 2022 at 11:13 PM.
Melting Slicks
Joined: Apr 2010
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From: Canberra Australia
2025 C3 of the Year Finalist - Modified
At some stage the domain entry or host will run out of subscription and they will all be lost.
I see they have a donate option to help keep it going but is that something Ernie set up of more recent ?
Last edited by CraigH; Dec 25, 2022 at 11:11 PM.
Team Owner
Joined: Jan 2007
Posts: 53,648
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From: Southern Cal Ca
St. Jude Donor '22
Thats not correct, the temp sender is a variable resistor, it varies the resistance to ground. ( the same as a fuel tank gauge. )
On the Will *** site they show a test procedure where you can substitute a variable resistor and check the gauge readings.
Check the 12volt supply to the gauge, also check that the gauges resistor is not shorted and mounted properly. Also check the ground wire to the gauge cluster.
https://youtu.be/LvW19Eu71P4
On the Will *** site they show a test procedure where you can substitute a variable resistor and check the gauge readings.
Check the 12volt supply to the gauge, also check that the gauges resistor is not shorted and mounted properly. Also check the ground wire to the gauge cluster.
https://youtu.be/LvW19Eu71P4
the vid at 4:20 shows what may be his trouble.
thanks for your detailed exception of my statements.
the last line probably
Thread Starter
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Joined: Aug 2021
Posts: 76
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From: Abu Dhabi
I think I’ll try to fix the old sending unit by refixing the connector head and see how it goes
I will keep you posted
buying a new sending unit from abroad which most likely that it will not work is a big risk and waste of money and effort
dont you think?
I will keep you posted
buying a new sending unit from abroad which most likely that it will not work is a big risk and waste of money and effort
dont you think?
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Joined: Mar 2017
Posts: 11,953
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From: Virginia
I came here to say this. Do you have a way to independently check your engine temp? In my 80, the gauge works perfectly (confirmed with an IR temp gun, and a modern 2-wire sender), but the needle still barely moves.
Otherwise, take the new sender, and the old sender, check the resistance at room temperature, and check again after boiling them in water. Same numbers? The problem is in your wiring.
The flexible circuit board behind the gauges is notorious for needing to be replaced.
EDIT: The PDF link posted by @BLUE1972 has what you need. You can fake any reading by replacing the sender with a resistor, or combination of resistors. For example, in boiling water, the sender should read about 100 Ohms. If you connect a 100 Ohm resistor to the end of the sender wire, and ground the other end to the engine, with IGN on, you should see the gauge at the second mark (the one after 200 deg, at 12-o'clock).
Be sure to download this PDF, and any others, while you can.
Otherwise, take the new sender, and the old sender, check the resistance at room temperature, and check again after boiling them in water. Same numbers? The problem is in your wiring.
The flexible circuit board behind the gauges is notorious for needing to be replaced.
EDIT: The PDF link posted by @BLUE1972 has what you need. You can fake any reading by replacing the sender with a resistor, or combination of resistors. For example, in boiling water, the sender should read about 100 Ohms. If you connect a 100 Ohm resistor to the end of the sender wire, and ground the other end to the engine, with IGN on, you should see the gauge at the second mark (the one after 200 deg, at 12-o'clock).
Be sure to download this PDF, and any others, while you can.
Last edited by Bikespace; Dec 26, 2022 at 08:23 PM. Reason: UPDATE
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From: Long Island
Given Willcox stopping operation how much longer will these docs be available ?
At some stage the domain entry or host will run out of subscription and they will all be lost.
I see they have a donate option to help keep it going but is that something Ernie set up of more recent ?
At some stage the domain entry or host will run out of subscription and they will all be lost.
I see they have a donate option to help keep it going but is that something Ernie set up of more recent ?
A wild guess, some company will "buy" the domain and videos then re-tag them. Lets hope.
Thread Starter
Advanced
Joined: Aug 2021
Posts: 76
Likes: 24
From: Abu Dhabi
I came here to say this. Do you have a way to independently check your engine temp? In my 80, the gauge works perfectly (confirmed with an IR temp gun, and a modern 2-wire sender), but the needle still barely moves.
Otherwise, take the new sender, and the old sender, check the resistance at room temperature, and check again after boiling them in water. Same numbers? The problem is in your wiring.
The flexible circuit board behind the gauges is notorious for needing to be replaced.
EDIT: The PDF link posted by @BLUE1972 has what you need. You can fake any reading by replacing the sender with a resistor, or combination of resistors. For example, in boiling water, the sender should read about 100 Ohms. If you connect a 100 Ohm resistor to the end of the sender wire, and ground the other end to the engine, with IGN on, you should see the gauge at the second mark (the one after 200 deg, at 12-o'clock).
Be sure to download this PDF, and any others, while you can.
Otherwise, take the new sender, and the old sender, check the resistance at room temperature, and check again after boiling them in water. Same numbers? The problem is in your wiring.
The flexible circuit board behind the gauges is notorious for needing to be replaced.
EDIT: The PDF link posted by @BLUE1972 has what you need. You can fake any reading by replacing the sender with a resistor, or combination of resistors. For example, in boiling water, the sender should read about 100 Ohms. If you connect a 100 Ohm resistor to the end of the sender wire, and ground the other end to the engine, with IGN on, you should see the gauge at the second mark (the one after 200 deg, at 12-o'clock).
Be sure to download this PDF, and any others, while you can.
done what was necessary, I was lucky to find an old 1980 Caprice with the engine out, borrowed the sensor and it worked just fine. An IR reading on the thermostat housing confirmed the reading on the gauge. I also removed the thermostat since she lives in a warm area.
thanks to all for your assistance and valuable help