Temp gauge mystery

-
I don't know if anyone mentioned it but I've heard that Teflon tape can mess with them. It is tapered pipe thread so that isn't needed
Another wives tail, the threads will cut through the tape or sealer and make a metal to metal contact.

Use an ohm meter between the base of the sender and the manifold you will get the same numbers as if you short the leads together.
 
I took ohm measurements on a new sender.

Screenshot_20250417-194251.png


The numbers in red are extrapolated from the resulting graph.

Screenshot_20250417-194500.png
 
Last edited:
Just my opinion, but I still think you have a bad sender at 300 ohms, and they are not logarithmic.
 

Just my opinion, but I still think you have a bad sender at 300 ohms, and they are not logarithmic
My chart is on the sender in my car right now before I installed it

Ok not logarithmic but not linear either, I guess that means it exponential ( a curve)

1744942955271.png


as I posted above but perhaps this is easier to read

room temp 70 deg is 346 ohms and 150 deg is 74 Ohms

1744943492116.png
 
Last edited:
I suspect you are right, and my memory is probably failing me. I just don’t remember the cold readings being that high. As I have gotten older, my memory is definitely not improving.

I agree that a sender operating like your charts should move the gauge around in a “normal” manner. If the gauge is not working at all, a sender like this is not the issue.

False alarm on my part.
 
Fascinating information from ya'll. Yeah, I'll keep poking around. I'll find out what is wrong. Seems weird though; gauge checks out, wiring checks out, and if the sender is good, as seems to be the concensus, what else is there?
I know one thing, I'll test them before they go in!
 
I've had 2 cars (71 Demon 318) and my now 73 340 that the temp gauge would swing rapidly from 1/3-1/2 of the normal gauge to all way hot to back to normal in matter of seconds. I sold the Demon way back in the day. For the 73 - I installed a Autometer eclectically gauge and it runs at 185-190 all day and is connect along with the factory gauge which barely gets to the first normal line. I have since changed the radiator when the temp gauge was swinging cause the previous owner had an undersized aftermarket installed in it.
 
That needle swinging sounds familiar. Mine does it similarly, except it starts doing that once the engine is hot and only does it after I stop it and restart it. All other times it sits at zero. That should be a huge clue as to what is going on here, but I'm not smart enough to figure it out.
 
There is a possibility that the sender wire is skinned and is making a short to ground some times under some conditions.

If both the temp and fuel did the same at the same time I would suspect the IVR but since they are not it must be in the sender, sender wire, bulkhead connectors, gauge cir board or gauge.
 
There is a possibility that the sender wire is skinned and is making a short to ground some times under some conditions.

If both the temp and fuel did the same at the same time I would suspect the IVR but since they are not it must be in the sender, sender wire, bulkhead connectors, gauge cir board or gauge.
I agree. I'll check all of those possibilities soon. I'm actually restoring this Dart and I'm up to my neck in preparation for paint. Thanks for all your help.
 
Intermittent problems are the most frustrating to troubleshoot since it always seems to work when you are looking at it. You might have a friend watch the gauge and start wiggling wires around wherever you can. Sometimes you get lucky and see problem appear.
 
I just jiggled the connector on the back of the cluster with the car warm and the gauge, which was dead, started working. Give it a try.

17450925941172385294512380041267.jpg
 
Wiggling and working suggests the pins on the cir board are not making a good connection.

Cur boards are available and OEM ones can be repaired
 
I had that cluster out recently and went completely through it. I doubt that's the problem but I could have missed something. Anyway, that's a great suggestion and I will take another look.
 
I had that cluster out recently and went completely through it. I doubt that's the problem but I could have missed something
The cir board on the bench and installed are two different animals.

Old wires applying pressures where they would not be on a bench
 
I had that cluster out recently and went completely through it. I doubt that's the problem but I could have missed something. Anyway, that's a great suggestion and I will take another look.
I put an electronic IVR in it and had the entire cluster out as well. Cleaned everything up and added a good ground. Frustrated that gauge would work sometimes. After reading your issues I thought why not go push all the connectors in? While the engine was warm and running I pushed and wiggled all the bulkhead connectors on both sides of the firewall, no change. Reached up behind the cluster and wiggled the cleaned connectors and the needle swept up to the middle! Woohoo!
 
I put an electronic IVR in it and had the entire cluster out as well. Cleaned everything up and added a good ground. Frustrated that gauge would work sometimes. After reading your issues I thought why not go push all the connectors in? While the engine was warm and running I pushed and wiggled all the bulkhead connectors on both sides of the firewall, no change. Reached up behind the cluster and wiggled the cleaned connectors and the needle swept up to the middle! Woohoo!
Congrats to that! Maybe I'll get lucky that way too. I'll certainly try it. I love those electronic IVR's. A little pricey but probably worth it.
 
If I ground the sensor connector and the needle lurches all of the way to the right, doesn't that indicate my connections are presumed good? (Question for Dana67, though anyone can answer)
 
If I ground the sensor connector and the needle lurches all of the way to the right, doesn't that indicate my connections are presumed good? (Question for Dana67, though anyone can answer
Typically that would indicate the gauge and relater wiring is functional.
 
Another cause for intermittent readings is from the sensor not immersed in the water, ie. low water level.

Here is my Mopar sensor calibration readings (see photo).
Ignore the voltage readings. They were obtained from a DC power supply rather then the factory IVR "chopper" circuit for regulation. It’s not possible to read voltage or current when using the factory type regulator.

Water Sensor Scale.jpg
 
Another cause for intermittent readings is from the sensor not immersed in the water, ie. low water level.

Here is my Mopar sensor calibration readings (see photo).
Ignore the voltage readings. They were obtained from a DC power supply rather then the factory IVR "chopper" circuit for regulation. It’s not possible to read voltage or current when using the factory type regulator.

View attachment 1716396764
Looks to be in align with readings others have reported. Thanks for sharing.
 
-
Back
Top Bottom