Temperature gauge does not work on my 1970 340 Duster ?

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Dave, I think I gave you bad instructions on #1. If you have the original regulator the voltage will vary like you have seen. Sorry, I was thinking about the replacement that is fixed at 5v. My mistake.

It looks like the voltage regulator is at least cycling and maybe working correctly.

Try step 2. If you ground each of the sensor wires the gauges shoul each go full scale.

Sorry for the lack of precision in the instructions. This kind of stuff is confusing in person, much more from a distance.
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Dave, I think I gave you bad instructions on #1. If you have the original regulator the voltage will vary like you have seen. Sorry, I was thinking about the replacement that is fixed at 5v. My mistake.

It looks like the voltage regulator is at least cycling and maybe working correctly.

Try step 2. If you ground each of the sensor wires the gauges shoul each go full scale.

Sorry for the lack of precision in the instructions. This kind of stuff is confusing in person, much more from a distance.
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No prob Mike, thanks for the update and confirmation the voltage readings appear to be good. I did ground the temp sensor wire and the temp gauge goes up to high/hot. I will have to ground the gas sensor wire ...but if that also works then ??
 
What I a. Trying to do is to divide and conquer. If we can see that grounding the sensor right at the gauge cluster works, the we move father away ( like maybe at the sensor connector on the block)and try it again.
 
Ok, if the temp gauge moves when you ground the wire at the block, looks like the circuit is good back to the dash.
 
It has been awhile on this, let me re read the thread & see what you have done so far.
 
Here is what I have done so far during troubleshooting this prob.

1) grounded the sending unit wire, gauge moves up to 'H' (means the gauge should be good)
2) replaced sending unit with a new unit, gauge does not move??
3) connected my orig sending unit to the sending unit wire and grounded the threads of the unit. Then heated up the sending unit, gauge registered/moved accordingly towards 'H' !

Why doesn't the gauge work with the original sending unit installed in the manifold??
Could the gauge still be bad even though it moves when grounding the sending unit?
Not sure if it is related but my gas gauge reads empty. I will try grounding its sending unit wire as well....any help would be appreciated.
Let's go back to square one..................see the photo?
c-3826-jpg-jpg-jpg.jpg


Those resistance values in yellow, someone edited that to reflect the factory tester values. If you can heat your old sender and get it close to one of those values, then stick it in the circuit from block to sender wire, and if the gauge reads somewhat close (of course it will change--------the sender is cooling down!!!

THEN THE ENTIRE GAUGE CIRCUIT is likely OK, or at least "OK enough" that you can move forward

I tried to tell you earlier..........with the engine "somewhat warm" take your meter and measure the resistance from the sender stud to the sender brass. That should give you some idea based on temperature (see the photo) of whether the sender is good

Measure resistance from the sender brass to some known ground........LOL....LIKE THE BATTERY NEGATIVE POST. It should be close to zero

Try subbing in the old sender and see if these values change.

ANOTHER THING you can try is to connect the temp sender (jumper clip wire) to the oil sender wire. THIS WILL TURN THE OIL PRESSURE GAUGE into a TEMPERATURE gauge. You can also do the opposite............jumper the temp sender wire to the oil sender and that should cause the temp gauge to read OIL PRESSURE
 
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What I a. Trying to do is to divide and conquer. If we can see that grounding the sensor right at the gauge cluster works, the we move father away ( like maybe at the sensor connector on the block)and try it again.
I did measure the voltage of the temp sensor right at the gauge cluster using the dash ground earlier so the dash ground s/b good. Not sure grounding the sensor with the dash ground will buy us anything?
 
Yeah, you’re right. I have forgotten a lot of the details of this puzzle.

One thing that I remember from my youth (I think) is that the temp sensors can be damaged by too much heat. If you are trying to simulate engine temp with a torch or a lighter, the sensor can be damaged and will go open I think. Don’t know if you have done this but worth mentioning.
 
To put this another way a standard dash with no oil pressure, or a ralley dash with oil pressure, both temp and fuel (and oil pressure) gauges ARE THE SAME. The same resistance at any sender will cause any of the gauges to act the same
 
Yeah, you’re right. I have forgotten a lot of the details of this puzzle.

One thing that I remember from my youth (I think) is that the temp sensors can be damaged by too much heat. If you are trying to simulate engine temp with a torch or a lighter, the sensor can be damaged and will go open I think. Don’t know if you have done this but worth mentioning.

I believe that's true, and they can also be ruined by over tightening
 
Very confusing. It seems like that when nothing makes sense it is often a bad ground, as currents can go ways they normally don’t go.
 
I believe that's true, and they can also be ruined by over tightening
Please note...I did not use a torch to heat up the temp sending unit. I heated up a cup of water and placed submersed it. I also have tried a brand new temp sending unit. I dont think I damaged the sending unit. So far I didnt touch the gas tank sending unit. At this time the oil pressure gauge works fine, but the gas & temp gauges do not work. All voltages at each sending unit appear to be good. By grounding the temp sending unit the gauge also seems to work (moves all the way to hot), I will try grounding the gas gauge sending wire, if the gauge works then it would suggest I have two defective temp sending units and a defective gas sending unit. As the dash ground checks out, and limiter seems to be putting out the proper voltage cycling.
Before replacing the sending units, I will perform the resistance measurements mentioned earlier by 67dart273. If they do not change (lower resistance) when heated, that will confirm the sending units are defective.
 
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Anything is possible with cheap Chinese crap nowadays. I would suggest that you follow 67 darts instructions exactly in order. I think he has a superior knowledge of how this works. I think I am just confusing the process trying to help.
 
No prob Mike, thanks for the update and confirmation the voltage readings appear to be good. I did ground the temp sensor wire and the temp gauge goes up to high/hot. I will have to ground the gas sensor wire ...but if that also works then ??
Is it possible that your engine hasn't made hot water enough to move that gauge needle? If the engine is up to normal operating temperature there should be somewhere between 40 and 25 ohms resistance between the senders contact post and chassis ground.
You don't absolutely have to go under the car to ground the fuel sender wire. It can be found in rearward harness connector behind left kick panel. Then again... To verify the ground jumper over the fuel senders hose connection and check all of the blue sender wire run, you must go under the car.
So why the service techs needed a 3 position tester... The sender wire direct to ground zero ohms test doesn't always prove good gauge. I've seen some that were soooo toasted inside that zero ohms could cause movement while within normal range ohms could not. Looking at those, the needle doesn't go all the way home at off. It'll stop very near the hash mark scale.
This 4th/off/home needle position isn't on the tester.
 
So why the service techs needed a 3 position tester... The sender wire direct to ground zero ohms test doesn't always prove good gauge. I've seen some that were soooo toasted inside that zero ohms could cause movement while within normal range ohms could not. Looking at those, the needle doesn't go all the way home at off. It'll stop very near the hash mark scale.
This 4th/off/home needle position isn't on the tester.

Exactly why I'm trying to get him to check sender with an ohmeter
 
Thanks but I doubt that the reason the gauge is not working when the engine is running, is because of low coolant. I checked coolant level, also that the thermostat opens and that it is not "vapor locked". Again when the engine is warmed up and running, the gauge never moves. But when you shut the engine off, and turn the key to the 'ON' position it will read the proper temperature. Start the engine and it immediately moves to the bottom or cool position.
I just re read this entire thread. I read the oil gauge works but have no clue how it works, what it reads.
The above post along with a couple others suggest a working but faulty mechanical limiter. It should produce a pulse voltage that can operate all 3 thermal gauges but it does put out a higher current during warm up period before leveling to the circuit demand. So maybe its' leveling to a very weak pulse voltage and that takes the path of least resistance to ground. Thus 2 or 3 volts going through the oil gauge at start up, leaving notta for the temp gauge.
There would need to be a serious fault in the oil gauge circuit for that to draw away all of a good limiters output but... maybe that is possible. I haven't seen every condition, every way a oil sender can feck up.
So just for knowing... disconnect the oil sender and isolate that wire terminal. Now lets see if the temp gauge responds differently. If it does, we know the fault is in amount of limiter output going to where? and why? to replace the oil sender wouldn't break the bank. If that yields no joy...
Next question is... Is the limiter truly bad or is it only lacking a good chassis ground? It gets its chassis ground via a small piece of metal on its back pressed against the inst housing and inst' housing screws to dash.
It is possible that all of these instrument problems are due to 3 loose mounting nuts on the fuel gauge.
I must add that if I determine the fault is inside the car, and I must pull the inst' panel and disassemble it, I will install a solid state inst' voltage regulator while I'm there.
 
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I just re read this entire thread. I read the oil gauge works but have no clue how it works, what it reads.
The above post along with a couple others suggest a working but faulty mechanical limiter. It should produce a pulse voltage that can operate all 3 thermal gauges but it does put out a higher current during warm up period before leveling to the circuit demand. So maybe its' leveling to a very weak pulse voltage and that takes the path of least resistance to ground. Thus 2 or 3 volts going through the oil gauge at start up, leaving notta for the temp gauge.
There would need to be a serious fault in the oil gauge circuit for that to draw away all of a good limiters output but... maybe that is possible. I haven't seen every condition, every way a oil sender can feck up.
So just for knowing... disconnect the oil sender and isolate that wire terminal. Now lets see if the temp gauge responds differently. If it does, we know the fault is in amount of limiter output going to where? and why? to replace the oil sender wouldn't break the bank. If that yields no joy...
Next question is... Is the limiter truly bad or is it only lacking a good chassis ground? It gets its chassis ground via a small piece of metal on its back pressed against the inst housing and inst' housing screws to dash.
It is possible that all of these instrument problems are due to 3 loose mounting nuts on the fuel gauge.
I must add that if I determine the fault is inside the car, and I must pull the inst' panel and disassemble it, I will install a solid state inst' voltage regulator while I'm there.
Ok thanks for all the input...I
I just re read this entire thread. I read the oil gauge works but have no clue how it works, what it reads.
The above post along with a couple others suggest a working but faulty mechanical limiter. It should produce a pulse voltage that can operate all 3 thermal gauges but it does put out a higher current during warm up period before leveling to the circuit demand. So maybe its' leveling to a very weak pulse voltage and that takes the path of least resistance to ground. Thus 2 or 3 volts going through the oil gauge at start up, leaving notta for the temp gauge.
There would need to be a serious fault in the oil gauge circuit for that to draw away all of a good limiters output but... maybe that is possible. I haven't seen every condition, every way a oil sender can feck up.
So just for knowing... disconnect the oil sender and isolate that wire terminal. Now lets see if the temp gauge responds differently. If it does, we know the fault is in amount of limiter output going to where? and why? to replace the oil sender wouldn't break the bank. If that yields no joy...
Next question is... Is the limiter truly bad or is it only lacking a good chassis ground? It gets its chassis ground via a small piece of metal on its back pressed against the inst housing and inst' housing screws to dash.
It is possible that all of these instrument problems are due to 3 loose mounting nuts on the fuel gauge.
I must add that if I determine the fault is inside the car, and I must pull the inst' panel and disassemble it, I will install a solid state inst' voltage regulator while I'm there.

Ok I verified one of the temp sending units is good (new one) by heating it up within a cup of water and the gauge moves accordingly, i.e. mid way at about 40 ohms. The resistance of the new sending (cold) is around 200 ohms. The old or original was about 2x, (400 ohms). I did heat it up as well and the resistance lowered but never hooked it up to the gauge. I also grounded the gas sending wire and the gauge did move all the way to full. I cannot start the car and bring it up to normal temp at this time because I am rebuilding the p/s unit. Once complete, I will start the car and check the temp gauge. It should work, if it doesnt??? I will isolate the oil pressure gauge from the circuit to see if it is somehow consuming all the voltage from the limiter. If it still doesnt work??
Note: I used the ground off the battery to check the temp sending unit and gauge circuit. This ground cable splits and is tied to the chassis as well.
 
Electrical Demon in my 72 Demon.
My temp gauge does not work. Fuel gauge does work. Here is what I have done after reading every thread I can find on the subject. Anything I might have missed please do not hesitate to comment. My Demon is all original no modifications

•Remove purple sensor lead and ground it at manifold, Gauge pegs out to 'H' in about 2 seconds
•Replace sensor. Still not working
•Check ohms of the sensor, reads 100 plus when cold, about 10 when hot, check. reference 67 Dart 273 post above for readings. Is there multiple sensors used in Mopar engines/years? Have the 340.
•Checked voltage limiter, volt meter inconclusive; cycle time is too fast for accurate reading. I hooked up bulb and I get steady cadence of on/off every second or so. 12 volt input to limiter is good @12 volts.
•Loosened sensor when hot to bleed any possible air gaps. Still not working.
•Pull block @firewall, Purple wire ohm reading the same as the sensor.
•Pull dash circle plug, purple wire ohm reading the same as the sensor
•When I plug in circle plug, ohm reading reads high but not stable; bouncing from 20's to 40's. HMMM??
•checked back board on dash, continuity good (no breaks)
Added secondary ground to dash board, still not working.

So sensor good, wiring good, Gauge good (maybe). Sensor ohm reading is good from sensor to circle plug. Ohm reading changes reading when gauge is plugged into the system, Normal?
I'd buy a new temp gauge but $130 and Classic Industries has
maybe a 20% success rate on its cheap China **** and no returns on electrical. Looked for a $20 gauge somewhere for testing, nothing found in 5/6 volt.

I don't have equipment to test the gauge. Any thoughts on;
•could the gauge be fried/bad and giving me a false positive when i ground purple temp lead?
•Is there an easy way to test gauge with home tools.
•What is thought on ohm reading changing when plugged into
Gauge.

Sorry for the long message. I'm trying to eliminate the obvious and things already tested. This looks like a true Demon in my Demon and hopefully someone on this forum has had the same and can share their remedy.
 
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I had the same issues with my temp gauge, I could never get it to work. I checked all grounds, heated sensor outside of car, replaced voltage limiter, it all tested good, still gauge did not work. I gave up on it, and just drove the car wit no temp. gauge. Eventually, it started working on its own, it took a while for the gauge to move, but it did work. The only thing I could come up with was low coolant, an air bubble, or something like that. After flushing the radiator and block, it seems to works fine now.
 
I had the same issues with my temp gauge, I could never get it to work. I checked all grounds, heated sensor outside of car, replaced voltage limiter, it all tested good, still gauge did not work. I gave up on it, and just drove the car wit no temp. gauge. Eventually, it started working on its own, it took a while for the gauge to move, but it did work. The only thing I could come up with was low coolant, an air bubble, or something like that. After flushing the radiator and block, it seems to works fine now.
Thank you DartLarry!
Very interesting, worth a try to do some more investigative stuff. Maybe add a pee bottle to the cooling system to help remove any residual air that may be in the system. It is not the stock manifold, maybe the Edelbrock design is prone to an air pocket in that spot. I did loosen the sensor and let the coolant flow out while hot and thought it was sufficient to remove any trapped air in that spot. Dry pocket would certainly affect the temp sensor but hard to believe the air bubble would stay there, the block generally will not hold an air pocket for long. I am planing on painting this car soon and it is my hope to have all the mechanics dialed in so the reassembly of the project was not met with repeated removal/reinstalls. I'm probably on r/r # 5 or 6 for the dash. Dropping the steering column each time. A last clean install after paint would be a good target.
 
There is only 1 temp sensor listed. The only difference is aftermarket quality.
The most important factor is water temperature. You must confirm that the thermostat is working and the water is in fact hot. Of all the gauges I serviced over a 8 year period only 1 was returned. That owner claimed the gauge reads waaaay too high. He didn't want to believe his recently rebuilt engine was running too hot. I proved again the gauge to be correct and sent it back to him
Is yours the opposite condition?
A digital volts meter on the mechanical limiter shows a lot of changing numbers. 2.XX to 3.XX that should average 5.XX volts. Most of us choose to replace that antiquated mechanical limiter with a modern solid state regulator. Several to choose from ( ebay ) starting at about 30 USD. Those are universal in design, thus requiring some alternate mounting and connecting by the end user. The only one that is nearly exact replacement for this application is about 55 USD ( RTE ). Plugs right in like OEM.
Any shop ( myself included ) that would service/repair your gauge(s) would demand a solid state regulator be installed. That steady stable output voltage that can be confirmed with a digital meter means fewer questions and extended gauge life.
 
There is only 1 temp sensor listed. The only difference is aftermarket quality.
The most important factor is water temperature. You must confirm that the thermostat is working and the water is in fact hot. Of all the gauges I serviced over a 8 year period only 1 was returned. That owner claimed the gauge reads waaaay too high. He didn't want to believe his recently rebuilt engine was running too hot. I proved again the gauge to be correct and sent it back to him
Is yours the opposite condition?
A digital volts meter on the mechanical limiter shows a lot of changing numbers. 2.XX to 3.XX that should average 5.XX volts. Most of us choose to replace that antiquated mechanical limiter with a modern solid state regulator. Several to choose from ( ebay ) starting at about 30 USD. Those are universal in design, thus requiring some alternate mounting and connecting by the end user. The only one that is nearly exact replacement for this application is about 55 USD ( RTE ). Plugs right in like OEM.
Any shop ( myself included ) that would service/repair your gauge(s) would demand a solid state regulator be installed. That steady stable output voltage that can be confirmed with a digital meter means fewer questions and extended gauge life.
Great insight RedFish. I will look for the solid state limiter. Please message me if you have a link to the one you used. Although my original still works I would like to eliminate any issue going forward. Back of my mind I've marveled at the success of the simple mechanical design. If it were to get stuck on 12v I would assume it to be a $250 trip at the auto part store. Like I noted earlier, the limiter was too short of a cycle to get an accurate reading with my multimeter so I only confirmed with a lightbulb that the cycle has a constant cadence.

I'm pulling the thermostat today to see what is happening in the vicinity of the sensor, and will test the sensor in a can of hot water to see if I can get a reading. DartLarry's message above has me thinking I'm getting air in the system causing an air pocket at the thermostat. I can't thank you gentlemen enough for your generous help. At 20 years old I only have the internet and people like you to get these types of things solved.
I'm at the 'shinny new tool box' part of my life and the best source is still the 'slightly rusty Craftsman tool box with super smooth roller drawers' kind of guys like you make it happen.
 
Great insight RedFish. I will look for the solid state limiter. Please message me if you have a link to the one you used. Although my original still works I would like to eliminate any issue going forward. Back of my mind I've marveled at the success of the simple mechanical design. If it were to get stuck on 12v I would assume it to be a $250 trip at the auto part store. Like I noted earlier, the limiter was too short of a cycle to get an accurate reading with my multimeter so I only confirmed with a lightbulb that the cycle has a constant cadence.

I'm pulling the thermostat today to see what is happening in the vicinity of the sensor, and will test the sensor in a can of hot water to see if I can get a reading. DartLarry's message above has me thinking I'm getting air in the system causing an air pocket at the thermostat. I can't thank you gentlemen enough for your generous help. At 20 years old I only have the internet and people like you to get these types of things solved.
I'm at the 'shinny new tool box' part of my life and the best source is still the 'slightly rusty Craftsman tool box with super smooth roller drawers' kind of guys like you make it happen.
update on the temp gauge ghost. I pulled the sensor and dropped it in a can of 212º water. It registers about 120º on the gauge. Ohms at .105, so either the gauge is out of calibration (not too likely) or the voltage step down is not outputting 5 volts. (40 year old part) I'm going to get a solid state converter and fingers crossed. Stay tuned.
 
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