'39 pontiac temperature sending unit

[chartown]

Does anyone know if there is a way to test a temperature sending unit without installing it in the engine? This is for a '39 Pontiac 8 cyllinder.
Thanks,
JT

[Larry]

It seems weird, but there are no real easy ways to test a temperature sending unit. Perhaps there are ohm readings or something, but probably only a manufacturer would have those.

So, the only way I know is the old -pan-of-hot-water-trick. Check the explanation and photo that follows that I found on the internet with a little investigation:

This boiling water accuracy test for the water temp gauge can be used with equal accuracy for mechanical and electric gauges. With electric Water Temp gauges, the test should be done after the gauge and wiring has been installed in the car. (Because a wiring problem could affect the gauge performance.) When testing electric gauges that are already installed and wired, we can bring the electric hot plate and cooking pan to the car. Either we can put an insulated cover on the air cleaner to support the hot plate, or put the hot plate on a stand next to the car.

GROUND THE “SENDING UNIT” WHEN TESTING ELECTRIC GAUGES

A very important part of the test procedure for electric gauges is connection of a ground wire to the threads of the water temp switch for the gauge. For this ground wire, the author uses a test lead with a cable clamp that was originally intended for use with small battery chargers. (Because it fits over the large diameter threads of the temperature switch, but a small alligator clip will not fit.) Connect the other end of the test lead to a good ground, in example a carburetor mounting stud typically works well.

Then, make an extension wire from the existing original wire that will allow the sending unit to reach the hot plate area. 18gauge, 16gauge, or 14gauge wire is fine for the job, and the calibration reading at the gauge will not be affected with the wire at extended length.

This whole procedure means having a gauge that is in the car and a thermometer in the water that you can compare the dash gauge reading to. Of course you can use a dash and sending unit that are both out of the car, but you'll have to hook up battery power and be sure that there aren't any resistors anywhere in the car system that will not be in the "external" test system. I doubt there is in a '39. It's quite simple like my '40.

This whole thing sounds pretty primative!

Just as an idea, perhaps Marx Parts (specializing in older auto electrical parts), one of our featured Commercial Suppliers giving our members a nice discount can help. You can locate Bob Marx by looking under "AFFILIATES" in the line at the top of the screen, and then under "Member Discounts" "Parts."

Keep us posted.