Temp Gauge

[Hawker7]

Is there a way to test the stock temp gauge in a 72? I don’t know if it was working on the old engine, but I’m trying to test it now before I start up my new engine and I can’t get a reading. I have a new sensor out of the head and have plugged the lead onto the sensor and have grounded the body of the sensor to the motor. I put some really warm tap water into a bowl and put the probe into the water but the gauge doesn’t move. I also noticed that on my old heads there were sensors in each head, so I’m not sure if one was for the gauge, and one was for the idiot light? I tried both leads but none seem to cause the gauge to move. I also get a reading of 11.4 volts from the sensor when it is cold and about 10.8 when I put it in tap water. Is that right?

[Longhorn Man]

The sender for the guage is the one on the drivers side. the one on the passenger side was for the TCS smog junk.
With the ignition witch on, remove the green wire from the sensor, and ground it. If the temp guage pegs out to hot, then the guage and wiring is all good.

[JimKshortstep4x4]

If you have an ohm meter and a resistance simulator you can check out the dash unit and the block unit.

The sensor in the block puts out a resistance of 200 ohms, (hot) to 900 ohms (cold).

Using the resistance simulator hooked up to the dash gauge in lieu of the sensor, you can vary the input of the ohms to see where the gauge reads.

Usually the block unit is the problem of the gauges not reading. I use the electric eye on the stove for a heat source while measuring the change of resistance as the sensor is heated up.

It is possible to get the wrong block sensor. NAPA has a cross reference of the resistance range of the various block units.

Jim

[Hawker7]

I tried grounding the wire like Andy said and it pegged in the red. I then tried some water off the stove instead of hot tap water and I got a reading in the middle of the gauge. I guess hot tap water isn't enough to move the needle much...