Temperature Gauge Issue

-
dillon14

dillon14

Well-Known Member
Joined
Jan 14, 2006
Messages
105
Reaction score
16
I have a 1973 Dodge Dart Sport 340. The only thing not working was the temperature gauge. I tested the gauge by grounding the push on plug and turned the key on. The gauge pinned to hot. Turned the key off and it went back down. I'm thinking that is easy, I need a new temperature gauge sending unit. I bought one at NAPA, installed it and nothing changed. The temperature gauge did not move. I grounded the wire again and it pinned the gauge. The sending unit was identical to the one I removed. I am now stumped. Can anyone help?
 
From the gauge to a good ground? The signal goes from the sending unit through the circuit board pins ( the ones in a circle) then to the gauge, The voltage limiter 5 v may be bad or the pin that it is on does not make contact will.
 
The sending unit is a controlled ground. Make sure the threads are clean and you're NOT using teflon tape on the threads. Make sure the port that the sender screws into is clear and not plugged up with rust and other garbage. Make sure your coolant level is up and there's no air pockets in the motor. Fire the engine and bring it up to temp. Is the gauge working now? If not, your new sending unit could be bad, too. Welcome to the wonderful world of aftermarket parts.
 
Last edited:
Lift the wire off the sender and measure voltage from the wire to ground, it should be 5v. if the regulator is good. If OK use a resistor or variable resistor to simulate the sender resistance. Maybe google the span of resistance from cold to hot to find what
resistance is needed. Did the sender ever work? could be the previous owner installed a sender with the wrong range, or there is teflon on the sender threads preventing a good ground connection.
 
It won't be a steady 5v due to the way the stock limiter works. Should see a "bouncing" 11-12 v. Some digital meters may smooth the signal, an analog meter will swing.
 
dillon14 said:
I have a 1973 Dodge Dart Sport 340. The only thing not working was the temperature gauge. I tested the gauge by grounding the push on plug and turned the key on. The gauge pinned to hot. Turned the key off and it went back down. I'm thinking that is easy, I need a new temperature gauge sending unit. I bought one at NAPA, installed it and nothing changed. The temperature gauge did not move. I grounded the wire again and it pinned the gauge. The sending unit was identical to the one I removed. I am now stumped. Can anyone help?
Click to expand...
 
There is Teflon on the new sending unit but a friend touched the plus side of the battery and the side of the sending unit with a test light and the light came on. He said the sending unit is grounded. Is he wrong? Is there a fuse that might cause the gauge not to work?
 
I have had more than one bad sensor new out of the box. The ones you buy at the parts store are crap. You might try an OEM one from a dealer.

If you measure the resistance of your sender with an ohm meter, it should read from about 60-80 ohms when it is cold. About 20-30 ohms hot with the car warmed. The bad ones I measured read about 2000, so an obvious difference.
 
dillon14 said:
There is Teflon on the new sending unit but a friend touched the plus side of the battery and the side of the sending unit with a test light and the light came on. He said the sending unit is grounded. Is he wrong? Is there a fuse that might cause the gauge not to work?
Click to expand...
If he went from battery + to the side of the sending unit, yes, the light should come on. It's going to ground, just like grounding it anywhere on the engine. But is it a GOOD ground? Get that teflon tape off the sending unit and out of the threads on the manifold. Then use an ohmmeter from the sending unit housing to the manifold. It should be at or near 0. Then you know you have a good ground. Then test the operation of the sender as Mike69cuda outlined. With the ohmmeter + lead on the sender lug and the - lead to ground, you should have (I'm taking Mike's word on this :) ) 60-80 ohms. Warm up the engine, and take the measurement again. You should have 20-30 ohms. If either reading is off, you have a bad sender. Period. As long as you confirmed a proper ground, and you have confirmed voltage and gauge response as previously posted, that's all it can be.
 
Also, when installing the sender, don’t over tighten. I have wondered if I might have damaged one installing it. But since I didn’t check the resistance before I installed it I don’t know.

if you have a push on electrical connector you pretty much can’t screw that up. However if you have a lug and a nut, don’t over tighten that either.
 
OK, tomorrow I’m going to take the Teflon off and try it again. If nothing then, I’ll have someone test the sending unit. Thanks for all the advise.
 
Something else required that hasn't been mentioned... hot water. If the thermostat is missing or stuck open it could take a very long time to make that gauge move.
As the sender heats its resistance should slowly change to somewhere around 30 ohms. this slowly warms the bimetal beam inside the gauge. Beam slowly bows to lift the needle. Instant zero ohms test can make a OEM limiter and/or gauge do things they wouldn't do in normal conditions.
If you have ohms meter you can test the sender before removing it, assuming its bad. Thermometer to check water temperature also.
 
dillon14 said:
OK, tomorrow I’m going to take the Teflon off and try it again. If nothing then, I’ll have someone test the sending unit. Thanks for all the advise.
Click to expand...
Just take a piece of wire and connect from the body of the sender to neg of battery to see if the gauge moves.
 
You must log in or register to reply here.
-

Back
Top