Temp sending unit problem
Thread Starter
Intermediate
Joined: Apr 2005
Posts: 42
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Temp sending unit problem
Need some help before I go crazy. Just installed a new temp sending unit in my '72. Prior to installing it I placed it in a cup of boiling water and it worked as expected - off by just a few degrees. Anyway, I installed it and it now it doesn't work. Since I know the sending unit and gauge are working, I'm thinking I have some sort of grounding problem involving the engine block. I am not using any tape on the threads. Is it possible that the block's threads could be corroded and keeping the sending unit from grounding properly? Suggestions? Thanks.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,847
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
ocstanley
I'm curious how you know it was only off a few degrees in boiling water? This makes no difference right now since the gauge is not working. I've posted a scale on here in the past about what the required ohm's per the dash unit should be and was just wondering if you used it.
If you pull off the wire to the sending unit and touch it to the engine the dash unit should peg hot. If you remove the wire from the sending unit the dash unit should go to the cold position.
If these test work, then your dash unit and wiring are fine and the problem is the sending unit. If they do not work, then you have an issue in the car wiring.
Are the other gauges in the dash still working.
The sending units are cut in N.P.T. threads and they are tapered. Corrosion in the block threads should not play any roll in this since the tighter you turn the sending unit the more the threads dig in!
Willcox Inc.
I'm curious how you know it was only off a few degrees in boiling water? This makes no difference right now since the gauge is not working. I've posted a scale on here in the past about what the required ohm's per the dash unit should be and was just wondering if you used it.
If you pull off the wire to the sending unit and touch it to the engine the dash unit should peg hot. If you remove the wire from the sending unit the dash unit should go to the cold position.
If these test work, then your dash unit and wiring are fine and the problem is the sending unit. If they do not work, then you have an issue in the car wiring.
Are the other gauges in the dash still working.
The sending units are cut in N.P.T. threads and they are tapered. Corrosion in the block threads should not play any roll in this since the tighter you turn the sending unit the more the threads dig in!
Willcox Inc.
Thread Starter
Intermediate
Joined: Apr 2005
Posts: 42
Likes: 0
Now I'm not sure what I have. When the engine is on and running for about 10 minutes, the temp gauge needle just clears the 100 degree marker. I placed a 75 ohm resistor across the wire leading to the temp sender unit and grounded it, hoping to get a reading of about 220 degrees. Result: The temp gauge read approximately 125 degrees.
Any ideas/suggestions? Thanks
Any ideas/suggestions? Thanks
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,847
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Roger is correct! Pull the dash unit out of the car and test the resistor. When the resistor is shot, about the highest reading you can get out of the gauge is 1/4 of it's full output.
This sure sounds like the gauge resistor is shot to me.
You have movement and response in the dash unit which tells me you have power to the gauge and a good ground.
You have signal making it to the gauge since you have movement. This all but eliminates everything else it could be. If you need this fixed you can pick up a resistor from your local electronics store.
Willcox
This sure sounds like the gauge resistor is shot to me.
You have movement and response in the dash unit which tells me you have power to the gauge and a good ground.
You have signal making it to the gauge since you have movement. This all but eliminates everything else it could be. If you need this fixed you can pick up a resistor from your local electronics store.
Willcox
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Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,847
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Willcox
