Temperature gauge calibration

Lawson Cox

Lawson Cox

Well-known member
Has anyone ever tried using dry ice where the temperature probe goes into the head to try and bring the fluid level in the gauge down? I have a NOS temp gauge in my pickup that runs at about 75% level in the tube and truck is running at maybe 165-175 actual temp. Before installing it I placed it in boiling water and it rose to top, and put it in ice water and it went to where could not see fluid. Will getting it down lower with dry ice and holding it there for a while help? Just pondering the issue. :confused:
 
Lawson, if there are air bubbles in the tube, you have to get them out. Test to see if there are bubbles by this method:

Remove the unit, glass tube high, sender low, with no loops in the line between. Boil the sender in water, and observe where the red liquid is on the glass bulb. Look closely at the glass bulb and you will see an etched line across the glass which indicates the factory calibration of 212º F. This location is where the red liquid should be.

If the liquid is above that etched line, you have bubbles. Dump it in ice water, back in boiling water, back and forth, hot and cold. Your dry ice may help in this method, I don't know.

Another way to skin the cat is to sqeeze the bubbles out with 10 G's force. Swing the unit around your head at full length of the tube, the sender bulb at the far end. Take caution that you do not stress the copper tube during this operation. This is the method that works for most guys.

After you get the bubbles out, take care that the glass tube never gets lower than the brass bulb again. That's how the bubbles got there in the first place.

Install the unit, and calibrate the etch mark with the 212º mark on the dash indicator. You'll then have the most accurate temperature gage ever devised. Another of Ford's better ideas.
 
Thanks Alan. Before I put it in the truck I hung it upside down for quite a while. I also put it in boiling water and then the freezer for a little while. That helped. I did not know about the etched line on the glass bulb. Can that line be seen with the gauge in the dash. I would hate to go to all the trouble to pull it out, only to find that it is where it is supposed to be.
 
Lawson, putting it in the freezer isn't going to do it. You need to always keep the glass high and the sender low, to allow the bubble to purge. By moving the liquid up and down the tube repeatedly with the boiling and the cold water, the bubble can gradually move up the tube, but won't move up without the help of gravity.

Yes, the etch mark is visible while in the dash, with a strong light and good eyes. The mark doesn't go all the way around the glass, so you may have to use a small mirror to see it. As you installed it yourself without calibrating, be prepared to make the adjustment while you're down there. You can't adjust it properly while installed, so remove the two screws that hold the indicator plate, and the whole thing comes off in your hand.

Better yet, grab one of those little girlies that insist on hanging around you and have her stand on her head to do the right thing. You can be there to watch and offer encouragement!
 
Thanks Alan. I may have to use the girls, they are almost short enough to stand up under the dash. LOL.

"the bubble can gradually move up the tube, but won't move up without the help of gravity." What kind of gravity do you have out there on the left coast? Huh??? LOL
 
Lawson, our gravity is seriously some heavy stuff. We don't take it lightly 'cause soon as we do, some concrete jumps up out'a nowhere and hits you in the head.
 
I will second Ford38V8's procedure for getting the air bubbles out of the bulb/tube. I hung my gauge up vertically overnight with the bulb down low and the cooper tube as straight as i could get it. Then , while keeping the gauge up high relative to the bulb, I transfered the bulb from a pan of hot water to a pan of ice water (about a minute in each) several times. I could see the air bubble come into the glass vial in the gauge and float to the top of the vial. At that time, I tested the gauge in boiling water and it was right on the money at 212.
 
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