original temp gauge

[ford38v8]

David, Sounds like you have a positive attitude about getting back in the swing of things!
The temp gauge is similar to a thermometer, having a bulb within the cooling system with liquid that reacts to temperature changes by expanding and contracting. A capillary tube connects that bulb to the gauge unit, where the liquid is visible through a glass on the capillary tube. The glass is calibrated at the factory with an etch mark at indicated 212º F., this mark to be lined up with the corresponding boiling point mark on the gauge face.

The liquid in this system is no longer available, due either to environmental or health risk issues. There are those who repair the system, and redish liquids are available to do it yourself, but none are equal to the original red liquid, either in color, or in the ability to remain visible, as the replacement liquid apparently settles out the color, or bleaches out to clear. Additional issues remain with calibration and sealing of the tube.

Reproduced units may be available from time to time, but have the same problems as described above, and are expensive. Original functioning units are also available if you look hard enough, but are even more expensive that the repos.

Now, a bit of good news possibly: If your tube still has the original fluid, but is way out of calibration due to air bubbles within, it is repairable without opening up the tube. Air tends to rise in liquid, meaning the tube that shows air bubbles has been out of service and improperly stored to allow those bubbles to appear. It has been stored bottoms up, exposed to multiple cycles of heat/cool, or bouncing around in a parts box for a long time. Reversing this process can take some imagination and time, but the reward is well worth the effort, and you get the bragging rights.

When you find one at a swap meet, you can check it out by surreptitiously slipping the sending unit into your cup of hot coffee. It should show movement of the liquid. A savvy vendor will have a pot of boiling water available for a proper test, or he may hold a lit match under the bulb. I wouldn't advise a cigarette lighter because a match will go out before any damage can be done, but with a lighter, who knows? Price? $$$ +?. Get well soon.