Three bad temp gauges in a row - any tips on how to adjust them?
 

Guys, I have a '51 with the original 6-volt system. All brand new reproduction wiring. I have a brand new sensor that bench tests perfectly.

My first temp gauge would pin to 'cold' with ignition turned on. A bench exam determined it was rusted inside and I put it off to the side. I then bought a used gauge and that one would read excessively hot (almost to the 'H' mark) at engine temp of 170 degrees at the thermostat neck and 130 degrees at the top hose to the radiator.
I bought a third used gauge and that one will read at the tick mark just beside 'H' at this same temp. So the third one is the best one of them all but I'd like to see the needle read in the middle of the range at this engine temp.

170 head temp seems ideal to me, it is what my engine will run at consistently. I want a completely stock appearance to the dash and functioning original gauges. Is there any way to adjust these '51/'52 gauges without breaking something fragile?
Open to ideas and suggestions.

Thanks,
Tom

There is an adjuster on the gauge unit, accessed thru a hole in the back of the case, see below. (this is a fuel gauge, but they are virtually the same)

Just to be clear, an engine that is "cold", not run all day, turning on the key should send the needle to C fairly quickly. Have you tried a different sending unit?

Hi Ross, thanks for the reply.
I have two sending units and tested them both on the kitchen stove(I posted a thread with pictures of the procedure a couple of years ago) and my new unit was the best one of the two.

I do not see that the temp gauge has the same access to the back as a fuel gauge does but will look closer after work today.

Tom

The hole may be covered with a little adhesive circle.

How could you test the temp sender in boiling water? Did you duplicate the entire system, gage unit, sender, 6v battery? That is the only way. They are not temperature-sensitive resistors like modern senders.

These are 6-volt gauges and should read ~ 1/2 scale with 1.5V applied and full-scale with 3V applied. They work off of heat via a bi-metallic spring. The gauge has a setting for both where it reads when "cold" and where it reads when "hot." By "cold" and "hot" I am not referring to a temp. gauge, just any gauge that has no voltage applied and is, thus, cold or that has voltage applied and is, you guessed it - hot.
The toothed adjustment on the "cold" side of the gauge, or zero-scale, is the adjustment for zero. The toothed adjustment on the "hot" side of the gauge is the adjustment for 1/2 scale. These adjustments have some interaction. Adjusting the cold setting, then applying 1.5V (as in from a bench power supply or a good (new) D cell battery) and adjusting the mid-scale setting should get these into calibration. I find that going back and forth between cold and 1.5V, and letting the gauge come to temp for several seconds, will give the best results. :-X06

A couple of notes - full scale (3V) tends to read a bit high when looking at several stock gauges, so, don't be surprised if you get the same results when you check yours at 3V. Also, use a volt meter to make sure that you actually apply the correct voltage. Polarity is absolutely of no consequence. These gauges use heat, so no worries about "hooking it up backwards." However, using an old "D" cell can cause the voltage to drop when the battery sees the load presented to it by the meter. In this case, the mid-scale setting would be incorrect. That is why I suggest using a new battery or power supply and checking the voltage with a voltmeter. Have fun! :-drink

Here is a link to the thread in which I tested my sender:

https://www.ford-trucks.com/forums/1...r-updated.html

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This is what I need, thank you very much. I hope to have time this weekend to work on adjusting the gauge.
I really want to know when this engine is operating at higher than normal temps. Not that it is a high risk problem in Maine...but....we do get our warm days and I hope to use the truck in a parade or two.

Tom

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Just wanted to follow up on my original thread.

I was able to adjust the gauge as Mr. Horvath spelled out and it worked like a charm.
Remove the two nuts and pull off the metal half-shield on the back and the two little holes will be visible. It was trial and error with a small jewelers screwdriver to adjust it where I wanted it.
At warmed up operating engine temp of 180 degrees my gauge now reads in the middle. Yesterday, after leaving a car show in the afternoon it was sunny and hot outside (Yes, 84 is hot weather in Maine :) ) I was moving as fast as I could on the highway so I wouldn't cause an accident - my top speed is 50 to 55 mph in a 70 mph zone and the 226 engine was working HARD with those 4:86 gears. The gauge read 3/4 range at that point. I shot a laser thermometer at the thermostat housing as soon as I got home and it read 190 degrees. So the gauge is perfect right now.

Thanks for the help.
Hope this helps if someone is searching a thread.
Tom

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This is REALLY good information and should be in a sticky or someplace where it can be found easily. Reps to you!

Great picture Ross!

Good to know. I'm subscribing so I can find this later. :-jammin

:-X22 Glad to share. I think that I will subscribe too. I forget things from time to time. BTW: the same design was used in later years but, at some point in the game, manufacturers switched to a 6 Volt full-scale system for 12 Volt vehicles. On these, you set 1/2-scale with 3 Volts. The system is cheap, simple, and effective. However, extremes of temperature in the dash environment can and will cause gauges to read a little off. This is normal and I think it's part of the personality of these old beasts.

I'm just wondering if this is what's wrong with my fuel gauge. It reads full before the tank is full. And it seems to zoom down to empty once it gets below half full. I had to replace the sending unit and have suspected maybe that's the problem. :-huh