Temp guage issue - Impala Tech
Electrical & Wiring Troubleshooting electrical problems

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post #1 of 7 (permalink) Old Yesterday, 09:19 PM Thread Starter
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Temp guage issue

Noticed the other day, that the needle on the factory temp guage
in my 68 was just about all the way up into the guage.
When i checked to see if the sending wire was connected to the
sending unit, it wasn't.
When I re-connected it, the needle went all the way into the top of the guage.
None of the needle is now exposed, the guage doesn't work. I checked the sending wire.
no breaks from what i can see. I changed the connector at the end of the wire.
What would cause the needle to disappear like this?
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post #2 of 7 (permalink) Unread Yesterday, 11:33 PM
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Usually it is a bad ground, but it could be a bad sending unit, or the wrong sending unit (since there are several). No way to tell over the internet.

There are different sending units to match the range of the gauge. There are sending units for idiot lights that trip a preset temp (one for too hot, another for too cold). There are sending units with a round "t" top spade, a flat spade, or a round pin.

This all assumes the gauge works.

All of these are electric and measure 0.5 V to 4.0 V if digital; or 1 V to 12 V if analog.

Asking me from Toronto what you have is like putting your hand behind your back and asking how many fingers are up?

I have know way of knowing.

Big Dave
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post #3 of 7 (permalink) Unread Today, 09:44 AM Thread Starter
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Dave, the guage was working up until a few days ago. The sending unit has been in
the current engine for years without a problem.
I checked the sending unit wire, it looks O.K. No visable damage, gave it a tug as it has a sheath around it,
no seperation. I even changed the female connector on the end to see if that was the case, nothing.
I have a seperate Auto Meter temp guage to the engine, however, it's nice to see all the factory guages working as well.
If the thing was working previously, one would think a ground issue. However, wouldn't that affect the other guages as well?
The others work fine.
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post #4 of 7 (permalink) Unread Today, 12:20 PM
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Could have a broken wire (open circuit). Have you check continuity with a meter?


Big Dave
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post #5 of 7 (permalink) Unread Today, 02:39 PM Thread Starter
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No, not yet. I'm suspecting the sender is bad. How do you check to see if it's working?
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post #6 of 7 (permalink) Unread Today, 04:43 PM
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Put the sender in pot of water and raise the temp while you measure the change in resistance. The sender is filled with a silicone based fluid that expands when heated. There is a pressure transducer in the top that changes resistance to ground as the pressure changes.

Big Dave
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post #7 of 7 (permalink) Unread Today, 06:04 PM Thread Starter
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Dave, even with the sending wire off the sender, the needle is all the way up
inside the housing on the cold side. The needle has completely disappeared.
It can't be the sender then, or else when you take the wire off, the needle would drop down a bit
and be visable...
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