Duster temp gauge problems

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dan0340

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Hey guys, I posted a question about this issue before and am still having issues even after suggestions. I have a 1973 Plymouth duster with a 360 la motor and an aluminum edlebrock intake. My temp gauge needle does not move at all. I grounded lead wire that goes to the sensor and the gauge works and jumps up to full heat. I’ve checked voltage at the wire and it is good. I tried 3 different sensors and the third being an OEM but still after running engine for a long time the needle doesn’t move! This car is a new project and I’m still discovering a lot about it. I’m thinking if looking at the thermostat. This seems like a far stretch but if the thermostat was stuck open could the gauge always read cold and not move at all? Or if there was no thermostat in there could that also cause this ? The fan is not electric. I got an aluminum radiator too. Thanks!
 
Almost sounds like a air bubble where the sender is. FYI the wire should have no voltage it works from the resistance of the sender think ground wire.
 
Agree. Works on ground. Did you Teflon tape the threads on the sensor? If so, you may not be getting a good ground on it.
 
halifaxhops said:
Almost sounds like a air bubble where the sender is. FYI the wire should have no voltage it works from the resistance of the sender think ground wire.
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Well when I took out the sender coolant came out like crazy so not sure on air bubble. As far as voltage on that wire I’m pretty sure it’s supposed to have small fluctuating voltage coming through the voltage limiter on the dash, that’s how it works with the gauge and the ground. At least that’s what I found from my research, someone can easily double check me with their set up. Just hook up a meter set to dc on that wire and then turn the key on and you will see voltage jumping around 5 volts going + or - a few volts.
 
Start by checking the sensor resistance. Here are the standard test resistors for checking gauges: IE the sensor should kinda match these at cold and operating.

You can tell if the sender is grounding by checking between the brass shell and the intake. Do NOT overtighten these. You can ruin them by doing so.

It is possible that even though the gauge pegs when grounded, it has a problem over the operating range, like, bent needle dragging on the gauge face, etc

c-3826-jpg-jpg-jpg.jpg
 
67Dart273 said:
Start by checking the sensor resistance. Here are the standard test resistors for checking gauges: IE the sensor should kinda match these at cold and operating.

You can tell if the sender is grounding by checking between the brass shell and the intake. Do NOT overtighten these. You can ruin them by doing so.

It is possible that even though the gauge pegs when grounded, it has a problem over the operating range, like, bent needle dragging on the gauge face, etc

View attachment 1716264102
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Yes that’s how I checked I had good ground and I know the sensor resistance is good as well. There is no way I could have three bad sensors including an OEM that were all new out of the box. No sure on the bent needle I guess. I wonder if there is a way I can mimic those resistances going back to the gauge to see if it moves at all
 
dan0340 said:
Yes that’s how I checked I had good ground and I know the sensor resistance is good as well. There is no way I could have three bad sensors including an OEM that were all new out of the box. No sure on the bent needle I guess. I wonder if there is a way I can mimic those resistances going back to the gauge to see if it moves at all
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Do you know if a stuck open thermostat would cause it to not move on the gauge?
 
All you can do is round up something to use for a test resistor. For a "quick" check, you could even heat a sensor up in water on the stove, then QUICKLY jumper it into the circuit and see if it reads upscale.

You could also heat them up and quickly check their resistance compared to the tester values.
 
The sensors are just thermistors, and they work across a very specific resistance-temperature range. Are you comfortable working with VOM's? If so, find yourself a 100 ohm (or higher) ohm pot (potentiometer), wire it such that it "replaces" the sensor (note quotes: the wire from your dash going "into" the pot, and the wire coming "out" of the pot should be on a good ground), and while turning the pot, have someone watch the gauge, as it should move smoothly across it's full sweep.

If it does, the gauge is ok.

Then, adjust the pot such that the gauge is near the middle of the range.

Remove the pot, check that resistance, and write that down.

Then check that your resistance across your sensor is compatible, or somewhat consistent, with the value your wrote down....which should also be somewhat consistent with the values in response #6. IOW, heat the sensor up to, oh, I don't know...175 degrees or so and then quickly measure it's resistance. (Or maybe do this first....)

My guess is the sensors you're buying are of the wrong resistance scale (incompatible with your gauge).

And as long as you have a good pot, you could always check the gauge "H" and "L" values as well, and then compare them to the sensors.
 
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DionR said:
Could a bad connection at the bulkhead cause this issue?
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Well the gauge pins hot when I ground the wire and I have voltage at the wire, I know the first two guys said there shouldn’t be any voltage with the sensor wire but I’m pretty sure there is supposed to be.
 
dan0340 said:
Well the gauge pins hot when I ground the wire and I have voltage at the wire, I know the first two guys said there shouldn’t be any voltage with the sensor wire but I’m pretty sure there is supposed to be.
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Just trying to think of other trouble spots along the way that might cause the issue. Thought maybe the ground in the sensor isn't good enough to get over the hump of resistance somewhere down (up?) stream.

Where did you get the OEM sensor? Was it used?

FYI, I'm struggling with a similar situation.
 
I bought
DionR said:
Just trying to think of other trouble spots along the way that might cause the issue. Thought maybe the ground in the sensor isn't good enough to get over the hump of resistance somewhere down (up?) stream.

Where did you get the OEM sensor? Was it used?

FYI, I'm struggling with a similar situation.
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the oem new on eBay. I think for my next step I’m going to look at the thermostat. Again the car is a new project to me and not sure it’s history. The wiring was a disaster but I’ve made a lot of progress. I can’t imagine that the needle wouldn’t even move if the thermostat was stuck open but I can’t think of what else is going on. I liked the idea mentioned earlier of putting the thermostat in a water at specific temps to see where or if it reads on the gauge. I can keep it attached to the wire and ground the outside and it should read if it’s a correct setup. Let me know if you figure out your issue. Do you have footage at your wire connection?
 
dan0340 said:
I bought

the oem new on eBay. I think for my next step I’m going to look at the thermostat. Again the car is a new project to me and not sure it’s history. The wiring was a disaster but I’ve made a lot of progress. I can’t imagine that the needle wouldn’t even move if the thermostat was stuck open but I can’t think of what else is going on. I liked the idea mentioned earlier of putting the thermostat in a water at specific temps to see where or if it reads on the gauge. I can keep it attached to the wire and ground the outside and it should read if it’s a correct setup. Let me know if you figure out your issue. Do you have footage at your wire connection?
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I meant voltage not footage
 
I always had a stock temp gauge issue with my '69, new sensor. We scrapped a '68 Cuda that had sat in the woods for 28 years. I grabbed the orginal sensor off of the 318, my gauge works just fine now. The new sending unit or sensor was junk. Checked the sending unit with a circuit tester, clipped circuit tester to pos battery terminal, sending unit to neg ground and circuit tester lead to terminal on sender. Wait for a dim light, no light, sender is bad.
 
dan0340 said:
I bought

the oem new on eBay. I think for my next step I’m going to look at the thermostat. Again the car is a new project to me and not sure it’s history. The wiring was a disaster but I’ve made a lot of progress. I can’t imagine that the needle wouldn’t even move if the thermostat was stuck open but I can’t think of what else is going on. I liked the idea mentioned earlier of putting the thermostat in a water at specific temps to see where or if it reads on the gauge. I can keep it attached to the wire and ground the outside and it should read if it’s a correct setup. Let me know if you figure out your issue. Do you have footage at your wire connection?
Click to expand...

Got a chance to look at mine finally and I have a good amount of teflon tape and high résistance between the sensor body and the intake. :BangHead:

I didn't check for voltage as I was a little frustrated with myself when I saw the teflon. But I am sure I would see 5v when the key is on.
 
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