1973 duster temp sensor question

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dan0340

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Hey guys, my first post here. I have no idea where im supposed to post this question. I hope this is the right place. I have a 1973 Plymouth duster with a 360la motor from some other unknown vehicle. The temp gauge is not working. It stays on cold and does not move. I have taken a jumper wire from the purple sending wire at the sensor and grounded it and the gauge jumped to all the way hot so I know the gauge is working. I replaced the sending unit or sensor twice but still does not do anything with engine running even though the engine gets warmed up. I tested voltage at the wire where it connects to sending unit and the voltage jumps around or fluctuates between a couple volts on up which I’m assuming is normal but not sure exactly. Can anyone give me an idea on what I’m missing here?
 
dan0340 said:
Hey guys, my first post here. I have no idea where im supposed to post this question. I hope this is the right place. I have a 1973 Plymouth duster with a 360la motor from some other unknown vehicle. The temp gauge is not working. It stays on cold and does not move. I have taken a jumper wire from the purple sending wire at the sensor and grounded it and the gauge jumped to all the way hot so I know the gauge is working. I replaced the sending unit or sensor twice but still does not do anything with engine running even though the engine gets warmed up. I tested voltage at the wire where it connects to sending unit and the voltage jumps around or fluctuates between a couple volts on up which I’m assuming is normal but not sure exactly. Can anyone give me an idea on what I’m missing here?
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I should add I got the vehicle this way. It hasn’t worked since I got it.
 
dan0340 said:
Hey guys, my first post here. I have no idea where im supposed to post this question. I hope this is the right place. I have a 1973 Plymouth duster with a 360la motor from some other unknown vehicle. The temp gauge is not working. It stays on cold and does not move. I have taken a jumper wire from the purple sending wire at the sensor and grounded it and the gauge jumped to all the way hot so I know the gauge is working. I replaced the sending unit or sensor twice but still does not do anything with engine running even though the engine gets warmed up. I tested voltage at the wire where it connects to sending unit and the voltage jumps around or fluctuates between a couple volts on up which I’m assuming is normal but not sure exactly. Can anyone give me an idea on what I’m missing here?
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Try removing any Teflon tape from the sending unit if it has any so that the sending unit makes a good ground connection. The threads are npt and do not require any Teflon tape/paste although I have seen it installed on them out of the box.
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I have had trouble finding good heat temp sending units, even the brand new ones are bad at times.

I usually test the sending units with a test light clamp on battery + positive and poke the send unit terminal.

The test light should glow if working correctly. The more the engine warms up the brighter the bulb will be.

Don't know if the send uints are for a gauge or an idiot light?

☆☆☆☆☆
 
What sensor are you using? i ran into the same issue with mine and the sensor ( sending unit ) would not work with my factory gauge i ended up installing a aftermarket bosch sensor and gauge. it works fine now. If your gauge moves with the wiring grounded it has to be in the sender. try and find an old original sender and see if that fixes it.
 
Even new ones can be iffy. The fluctuating voltage is perfectly normal. The problem has to be with the sender if grounding the wire gets the gauge up. Are you sure that the sender itself is grounding as it should?
 
George Jets said:
I have had trouble finding good heat temp sending units, even the brand new ones are bad at times.

I usually test the sending units with a test light clamp on battery + positive and poke the send unit terminal.

The test light should glow if working correctly. The more the engine warms up the brighter the bulb will be.

Don't know if the send uints are for a gauge or an idiot light?

☆☆☆☆☆
Click to expand...
It’s the gauge in the dash not a light. I’m wondering if the voltage is off?
 
remytherat said:
Even new ones can be iffy. The fluctuating voltage is perfectly normal. The problem has to be with the sender if grounding the wire gets the gauge up. Are you sure that the sender itself is grounding as it should?
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Is there a better way to test the sender? It’s just strange cause I bought two different senders from two different companies but they both didn’t move the needle at all
 
dan0340 said:
Is there a better way to test the sender? It’s just strange cause I bought two different senders from two different companies but they both didn’t move the needle at all
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What brands? You need to try an oem original one.
 
Honestly I feel like its not grounding to the intake. Take a spare sender and hook it up to the cable and then hold the threads to some exposed metal and see if you get some action.
 
OK how it works is like this the range on the sender is 10-73 ohms and where it is at sends the proper resistance to the gauge which runs on 5VDC through the current limiter. You can check them with a ohm meter say hot and cold to bench check them.
Hope it helps.
uage ohms.jpg
 
remytherat said:
Honestly I feel like its not grounding to the intake. Take a spare sender and hook it up to the cable and then hold the threads to some exposed metal and see if you get some action.
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Ok, I’ll try that, that should have been an obvious thing for me to think of!
 
halifaxhops said:
OK how it works is like this the range on the sender is 10-73 ohms and where it is at sends the proper resistance to the gauge which runs on 5VDC through the current limiter. You can check them with a ohm meter say hot and cold to bench check them.
Hope it helps.
View attachment 1716260776
Click to expand...
Thank you! Would it be not responding properly if the volt limiter wasn’t working properly? My gas gauge works though, and the temp sensor did ping all the way to hot when wire was grounded so I’m guessing it is an issue with sender. I’ll try to track down an oem
 
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