Bouncing temp gauge needle

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68dartgtman

68dartgtman

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Hey Guys,
just finished putting a new temp gauge in the cluster of my 68 Dart GT - old one didn't work but once and then never again - bought the new gauge from Classic Industries - everything hooked up and cluster back in dash. When I turn on the key - the temp gauge needle goes all the way over to "H" and then comes down but starts bouncing - start the car and it continues to bounce - all other gauges are working like they should. This has a non rally cluster.
Any ideas? I've never seen this before !
thank you very much!
 
I have not seen that, but I think the temperature sensor is a NTC resistor that decreases resistance with temperature. That means that if the engine is cold when you turn the key on, the reading should start low, not high. A short in the temperature sensor wiring to ground, would result in a high reading. The bouncing is a bit unkown, but the instrument regulator, can exhibit that behavior.

RedFish is a FABO member expert on instruments, wiring , and much more.
 
KitCarlson said:
I have not seen that, but I think the temperature sensor is a NTC resistor that decreases resistance with temperature. That means that if the engine is cold when you turn the key on, the reading should start low, not high. A short in the temperature sensor wiring to ground, would result in a high reading. The bouncing is a bit unkown, but the instrument regulator, can exhibit that behavior.

RedFish is a FABO member expert on instruments, wiring , and much more.
Click to expand...
Hey KitCarlson - thank you - the engine was warm because I started the car to warm up because I needed to turn the car around in the garage - plus it had not been started in about a month since I was upholstering the seats and repair the dash paint at the bottom of the cluster where I had messed that up taking the cluster in & out - this episode was the forth time the cluster has been out of the dash - I just tried it again as the engine is cold now and the gauge is still doing the same thing - hopefully RedFish will respond as I am at a loss as what it could be......you mentioned the instrument regulator...... is that the IVR ?
thanks again
Mike
 
IVR is the instrument voltage regulator. It is a bi-metalic thermal switch that regulates that average voltage based on on-off duty cycle. The gauge operation is thermal, the meter movements are driven by thermal expansion. The IVR pulses, but due slow thermal nature, bounce is not typically a problem, if the switching frequency is high enough. IVR can wear over time, and fail, but I would think the rest of the gauges would bounce too, fed from same regulator.
 
KitCarlson said:
IVR is the instrument voltage regulator. It is a bi-metalic thermal switch that regulates that average voltage based on on-off duty cycle. The gauge operation is thermal, the meter movements are driven by thermal expansion. The IVR pulses, but due slow thermal nature, bounce is not typically a problem, if the switching frequency is high enough. IVR can wear over time, and fail, but I would think the rest of the gauges would bounce too, fed from same regulator.
Click to expand...

Thank You KitCarlson- thanks for explaining - I guess I will start by tracing wires an checking grounds to make sure those aren't a factor

thanks again!
Mike
 
Ivr feeds only fuel and temp gauges.
Disconnect temp sender wire at gauge. Bounce quits replace wire or sender. Can ground sender and see if gauge stabilizes.

Those dash components are fragile,if it was mis handled during shipping that could be the cause.
 
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