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Old 02-07-2011, 04:10 AM
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Inoperative Water Temperature Gauge

My newly acquired '34 ford has an electric fan and the temp gauge worked fine until one day I forgot to turn on the fan and my motor overheated. After waiting couple hours to cool the motor down, I started the car and the gauge never worked. I changed the sending unit 2 times by purchasing the original and another name brand, still inoperative. Can anyone give me some tips?

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Old 02-07-2011, 04:23 AM
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If its a stock style temp gauge, testing the wiring is fairly simple.

Pull the wire off the gauge and with the ignition on, put a voltmeter on it. You should have voltage. If not, you have a blown fuse, broken wire, or an open circuit in the gauge (not real likely).

Pull the wire off the sending unit, and with the ignition on, ground the wire to the frame or block. That should make the gauge read the max.
- If that does not work, the gauge is bad.
- If that does work, you have a bad sending unit, or a bad ground between the sending unit and the engine (maybe you used teflon tape to seal the threads?).

You also can troubleshoot the gauge calibration by using known resistor values between the sending unit wire and ground - for example many GM gauges use a 0-90 ohm sending unit. Some OEM gauges have calibration markings to match certain resistor values, but you would need a service manual to get the values.

Bruce
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Old 02-07-2011, 04:39 AM
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Appreciate it.

Thanks Bruce, I'll try your remedies and let you know how it turned out.
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Old 02-07-2011, 05:01 AM
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One correction - In my first troubleshooting step what I meant to say was pull the wire off the sending unit and check for voltage with the ignition on. That verifies there is power from the fuse box, through the gauge and sending unit wiring to the sending unit.

Bruce
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Old 02-07-2011, 05:07 AM
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Okay, I'll do that first. Appreciate it.
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Old 02-07-2011, 06:34 PM
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Did you use Teflon tape when you replaced it. If it is a single wire sender and you used tape it may not work as it depends on thread contact for the ground.
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Old 02-07-2011, 08:44 PM
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It is a single wire connection to the sending unit and I didn't use any tape on the threads. I'll try that first. Thanks.
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Old 08-26-2011, 05:13 AM
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Found the problem

On the 454 LS6 there were 2 sending units mounted. One on the driver's side of the motor on the head next to the headers and one on the intake manifold. Apparently, the one on the head was the functional sending unit that malfunctioned. So I plugged that one and used the intake manifold plug instead.
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