oil temp combo gauge bench testing, what am I doing wrong (question answered) next: calibrate the gauge Options

[malcolm2]

I have had this gauge for a while. I also found the complete taco plate, sender etc... to set it up. I decided to test it. I tested the sender a while back in hot water and remember getting various readings as the temp increased.

I pulled out my 12v powered drill battery, put 12v + on the + terminal of the gauge and the - on the - of the gauge. ( you can't see the - wire in the picture, but it is there)

The gauge moved to where it is in the picture without the sender even being connected. It did not move once the sender was connected.

Inside the temp gauge are the following #s. Far left 30, at the start of the red line 156.7 and the end of the red line 170 *C

The top of the paper is what is stamped on each face of the hex and the gauge part # has been edited to what you see in the picture.

1. why is the gauge moving at room temp with or with out the sender?
2. do I have this thing hooked up right? any alternate testing suggestions?
3. do I have a matched sender & gauge?

[timothy_nd28]

You should test the potentiometer first. Measure the total resistance of the pot by checking the outer terminals, it should measure 1k (1000) ohms.

If this checks out fine, then put one meter lead to the middle pin, and the other meter lead on one of the 2 remaining pins (you choose). The pin that is not used, go ahead and bend it over so you don't get confused with it later. With the multimeter still on the resistance setting, observe what it is reading. Then turn the potentiometer fully in one direction, it will either read zero or 1000 ohms. Go ahead and turn it so it reads 0 ohms,,essentially a shorted state.

If all of the above checks out, and the potentiometer is calibrated to 0 ohms, continue to the next step.

As in post number 18, set it up the same exact way. The sensor casing is ground, and should share the same ground as the gauge ground and battery ground. The terminal on the sensor should be wired straight to the G terminal. Go ahead and boil a pot of water and verify everything still works as it did in post 18.

If all checks out and works like it did earlier, then wire in the potentiometer. The terminal from the sensor needs to be wired to the middle pin on the pot. The other pin of the potentiometer needs a wire going to the G terminal on the gauge. With your multimeter, measure the resistance from the G terminal on the gauge to the terminal on the sensor. You should read 0 ohms.

Now boil some water, and insert your sensor into this bath of water. Be sure that the sensor doesn't touch the sides or bottom of this boiling pot of water. You gauge should still reach the same red mark as you showed us in post #18.

Now, adjust the potentiometer, by adding resistance, you should see the needle back off from the red mark.