1947 Ford Temperature gauge question.

I am brand new to this forum, and trying to help my father-in-law with his instrument cluster. The temperature gauge was broken and I bought a replacement gauge on ebay. When it arrived, the gauge read on the "Hot" side of the gauge. I hooked up the gauge and started the engine and as the engine warmed up the gauge needle went to the cold side. I did not really drive the car to really get it hot.

My question: Should the gauge indicate "Hot" when it is cold (not running)?

I have looked at other instrument clusters for sale on ebay etc, and they all show the needle indicating hot.

Any assistance would be really appreciated.

Am a little confused here. Are you saying...At start up the gauge went to cold and starting going up from there or at start up the gauge read hot and went toward cold as the engine heated up. What the gauge reads with engine off is not that important, with engine running is the important part. Over the years manufactures have built gauges, oil pressure, engine temperature, even fuel level gauges, that read different if power is off to the gauge. This is because the sensors react differently to pressure, temperature, or fuel level. The more modern type of sensor is a variable resistor. Some move up in resistance as the temp., press., fuel level increase, others move down.

As an example is the fuel sender. Many cars today use a 0 (empty) to 90 ohm (full) sender. My 39 Packard is 78(empty) to 8 ohm (full). That's why you see so many questions about...what is my gas gage not reading correctly.

Thank you for your response Beltfed. At startup before the ignition is turned on and the engine started, the gauge registers "Hot". I haven't actually driven the car with the gauge installed, but when I turn the engine on and let it run (idle), the gauge descends to the "Cold" side (approx. 2-3 mins. of run time). When I turn off the engine and take the key out of the ignition, the gauge returns to "Hot" and stays there. Do you think that I am just not giving the gauge enough time to register the correct temperature reading?

I am not a Ford man. With that said I would think your O. K. Hopefully a Ford man will come along a set it straight. I suggest you start the car and bring it up to operating temp and see what your gauge reads. Post this and will go from there. Good luck.

Thnx for your imput. When I get a chance, I will take the 47 out for a drive and see what happens. Will post the results when possible.

Thnx again...

Update on the replacement gauge: Ran the engine for 10 miles and the gauge went from "Hot" to "Cold" and stayed there. Not sure what the issue is... Even reversed the connections on the gauge and it did the same.

Check to see if it is wired correctly on the engine.

There is a temperature sensor on the drivers side head and it must have two terminals on it. One terminal has the wire coming from the gauge fixed to it and the other terminal connects to a wire that goes over to the other head and this one has the single wire connected to it. If it is not hooked up correctly you will get a false reading.

I am assuming the sensors are the variable resistance type. To test the gauge itself (not the sensors). Disconnect the wire at the sensor that goes to the gauge, key switch on. The gauge will peg either empty or full. Now ground the wire going to the gauge, again key switch on. The gauge should peg in the other direction. If that doesn't happen your problem is either the gauge, the wire to the gauge, or a ground problem to the dash. If the gauge responds correctly then your problem is the sensors as David said above. One thing to check. Make sure the PO didn't use teflon tape on the threads of the sensors. The sensors must be grounded by the threads. Good luck.

Thanx for all of the useful information, especially about checking the gauge for defects. I should have let the forum know that the 47 Ford does not have a flat head engine. My father-in-law has swapped it with a small block chevy engine circa late 80's. I don't know if that has anything to do with the issue or not. The electrical has been converted to 12 volt with a converter for the instruments to 6 volt. I wish that I could be more informative about specifics, but will try to be more concise in future posts. I will let you all know what tests of the gauge determine when I can. Thanks again for all of your input and advise.

The small block chevy only uses one sensor. Mine is located on the intake manifold in front of the carb.