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Old 10-11-2020, 10:53 PM
70KLW 70KLW is offline
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Default RAIV Operating Temp

I have a 70 RAIV Judge. I am looking for suggestions on where to start with trouble shooting my temp issue? At start up the gauge is at zero but never gets hotter than 130-140 degrees. I appreciate any help. Thanks
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  #2  
Old 10-11-2020, 11:24 PM
Joe's Garage Joe's Garage is offline
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Default Have you checked the ACTUAL temperature of the engine or radiator?

The factory Rally gauges are notoriously inaccurate.

Good luck.

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Old 10-12-2020, 12:08 AM
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getmygoat getmygoat is offline
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Put a mechanical temp gauge on it first - or use one of those infrared thermometers.

After that it could very well just be a bad thermostat or even missing one. Check to see if you can see coolant moving by removing radiator cap immediately after cold start. if you see flow, your thermostat is caput.

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Old 10-12-2020, 08:35 PM
tekuhn tekuhn is offline
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The thermistor in the sending unit decreases resistance as the temperature rises. At 75degrees it should measure about 400ohms. At 160degrees it should be less than 50 ohms. If you don’t have a meter to measure the sender resistance to ground, then just ground the wire and make sure the gauge swings past full hot. That will let you know if you need to replace the sender or troubleshoot the gauge. Not sure, but that gauge might have a shunt resistor on the back posts that can go bad.

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Old 10-14-2020, 08:41 AM
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Formulajones Formulajones is offline
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This ^^^

I recently went through this on a Chevrolet and found the sending unit testing correctly. This particular model does have the resistor on the back of the gauge as Tekuhn mentioned. They come in various resistance levels and are usually color coded. Changing this resistance will dial in where the gauge reads.

The problem is though that I could never find a place that was reproducing these little color coded shunt resistors as Tekuhn calls them.

What I've thought about doing is installing an adjustable or variable resistor or potentiometer that will allow me to dial in the temp setting to match the actual engine temperature. Easy to wire in.

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Old 10-14-2020, 09:41 AM
tekuhn tekuhn is offline
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You might recall "back in the day" these resistors were pretty common in the Help! section at your favorite auto parts store to fix your gas gauge when they went bad and would work intermittently. They fail because they have the carbon trace printed on a ceramic bar, and over time the expansion/contraction caused the printed trace to crack - usually where they met the metal ends. After they got hard to find, I used to buy a standard 1-watt resistor in the correct value and added ring terminals to the leads and put those on the gauge to fix them. It's called a shunt, because it's connected in parallel with the gauge as a bypass so that 100% of the current isn't passing through the meter movement. The good old days of analog circuits and meter movements. These days if you have what appears to be an analog gauge, there's a good chance it's really a digitally driven stepper-motor unit.

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Last edited by tekuhn; 10-14-2020 at 09:57 AM.
  #7  
Old 10-14-2020, 10:56 AM
70KLW 70KLW is offline
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Thanks for the input guys! I haven't had the car long and was hesitant to drive it with out knowing what the actual temp of the engine was. I will put the car away for the winter in the next couple weeks and figure this out in the spring. Would you guys recommend not driving until its fixed or am I overthinking it?

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Old 10-14-2020, 11:03 AM
tekuhn tekuhn is offline
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Idle the engine with the radiator cap off and make sure you see circulation when it warms up to verify the thermostat is functioning. If it is and you're getting good heat exchange off the radiator, I'd certainly drive it with some caution and limitations on how far away from home I got.

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  #9  
Old 10-14-2020, 11:27 AM
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Quote:
Originally Posted by tekuhn View Post
You might recall "back in the day" these resistors were pretty common in the Help! section at your favorite auto parts store to fix your gas gauge when they went bad and would work intermittently. They fail because they have the carbon trace printed on a ceramic bar, and over time the expansion/contraction caused the printed trace to crack - usually where they met the metal ends. After they got hard to find, I used to buy a standard 1-watt resistor in the correct value and added ring terminals to the leads and put those on the gauge to fix them. It's called a shunt, because it's connected in parallel with the gauge as a bypass so that 100% of the current isn't passing through the meter movement. The good old days of analog circuits and meter movements. These days if you have what appears to be an analog gauge, there's a good chance it's really a digitally driven stepper-motor unit.
Yep those things are pretty much non existent now. I haven't seen them in years and showing one to a parts counter guy gets funny looks these days.
Most all the old Chevrolet muscle cars I've seen have them, so I would assume Pontiac used them as well. We have a factory gauge cluster for a 69 GTO here, I'd have to dig it out and look.
At the time they were available they were great, you could play with different colors and find one that corrected the gauge reading. I'm actually surprised the aftermarket hasn't caught on to those. They make everything else related to gauge clusters, gauges, printed circuits, lenses, housings, wire harnesses, etc... But these resistors are extinct.

The adjustable or variable resistors are pretty cheap to buy. I've actually worked on a couple of cars in the last few years where these were wired into the temp gauge and used to correct the reading so it's something people have been doing a long time already. As long as you don't mind making a couple wires to connect to the threaded stud terminals and having that device behind your dash, not a big deal really.

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Old 10-14-2020, 02:56 PM
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Peter Serio Peter Serio is offline
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Be mindful that most gauges from 50 years ago are in failure mode. When GM made the gauges inside where the moving parts are they placed 3 drops of glycerin "buffering" fluid. After many years that will leak out. Any GM gauge missing it's buffering fluid will fail.

The first mode of failure is a skew of the pointer display relative to the interior calibration of said gauge. This is a very common problem on these type of gauges. Especially a coolant temperature gauge. Soon after the pointer will detach itself from the shaft. Messing around with the resistor on the back of the gauge does nothing to address the missing buffering fluid issue.

A GM car gauge cannot survive if it is missing it's buffering fluid.

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