56 Pontiac Heat Gauge

Does anyone know where I could find a repair kit or new heat gauge sending unit for my 56 Star Chief? I have looked around and can't seem to find the mechanical style that will work with the original gauge. Any help would be appreciated!

 

Temp gauge, the correct one, is one unit and once cut is ruined. May be easier to remove the gauge and have it converted to electric and use a Chevy sending unit with it.

 

Found this somewhere, don't know who wrote it to give credit.


Repairing a Temperature Gauge

This article is meant to provide guidance for anyone willing to try and repair their own temperature gauge. If you would like to have your gauge repaired by a professional, I will undertake the job. Cost is $80, not including the spare gauge required to donate the good bulb and fluid. I guarantee the work for 90 days, and I calibrate your gauge for you. Just send me an email to get started.

Background

This article provides information on repairing capillary-type temperature gauges (pressure gauges) commonly found in automobile and aircraft applications.
Capillary type gauges utilize a Bourdon tube mechanism, and do not require electricity to function.
Temperature gauges used in aircraft and automobiles are of two general types: electrical, or pressure type. The electrical temperature gauge relies on a sender unit connected via wires to the gauge head. The sender produces varying electrical resistance according to the temperature it encounters. The gauge measures this resistance, and generally displays the difference by moving a needle on the gauge face.

The pressure type temperature gauge uses a Bourdon tube mechanism. This mechanism has been around since 1859 and was used in steam gauges, and continues in use today.
The Bourdon tube mechanism, or pressure gauge, has a gauge head with a needle which moves against a scale. The head of the gauge is connected to a very small diameter tube, which terminates in a bulb, or small reservoir which is immersed in the liquid (oil, steam, or coolant) whose temperature it will measure. The tube which connects the bulb and the gauge head is called a capillary tube, and it is hollow.

Principal of Operation

The Bourdon tube gauge actually measures changes in pressure within the capillary tube and bulb assembly. This assembly contains a gas which expands with heat, and contracts with cold, and thus moves a needle indicator.
The bulb, or gas reservoir, is immersed in the stuff whose temperature needs to be monitored. When the water or oil surrounding the bulb is hot, the pressure inside the gauge's capillary tube expands against the moving needle in the head of the instrument. Cooling the captive gas does the reverse.

What Goes Wrong

The capillary tube and bulb assembly are somewhat delicate items. They typically fail due to either vibration stress over a long period of time in service, or due to twisting forces applied when an old assembly is removed from a corroded engine or cooling system.
Many times if the break in the capillary tube is not complete, there may be no way for the naked eye to see the break in the tube, yet the unit will not function. The break only need be large enough to release the gas which was under pressure inside the bulb and tube assembly in order to fail.

WARNING

The gas contained in these instruments is very flammable! DO NOT attempt this repair near any open flame. DO NOT use a gas torch for soldering in this repair!

On U.S. certificated aircraft, only FAA certified instrument repairmen can repair aircraft instruments. Anyone else undertaking the repair of an aircraft instrument jeopardizes the airworthiness and safety of the aircraft. The author does not advocate illegal repairs.

Making the Repair

In order to repair the broken pressure-type temperature gauge, we will splice the old instrument head to a new capillary tube and bulb.

Materials

From your existing non-functioning gauge, you will need to retain the gauge head, and any fittings used to secure the bulb of the gauge into the oil or water.
Additionally you will need:

1. A length of copper tube with an inside diameter just slightly larger than the outside diameter of the capillary tubes you will be splicing. Three to four inches in length should be adequate. I have found 3/16" copper tube available from home supply stores meant for water supply line to work well.
2. A donor gauge, preferably new. Automotive supply stores typically sell water temperature gauges for around $20 (2008 prices) complete with hardware for securing the bulb into a tapped hole. Be certain that the donor gauge has sufficient capillary tubing to go from the gauge head to the bulb insertion point.
3. Solder and flux. Use the same solder used in common water supply line plumbing.
4. A container of about 1 quart in size.
5. Ice, water, and salt.
6. Tubing cutter.
7. Welding torch tip cleaners.
8. Emory cloth, fine or medium.
9. Soldering iron.
10. Shrink tubing to fit over the copper tube, plus 2 inches total length.
Repair Process

Examine the broken capillary assembly carefully to determine where the break occurred which has caused the gauge to fail. If the capillary failed at the head of the gauge, it will be a more difficult repair, but not impossible.

You can splice the capillary tube at any point you wish as long as you remove the break in the capillary tube from the old assembly. I prefer to replace as much of the old capillary as possible, ending up with as much new material as possible.

1. Cut off the old capillary as near the head as you wish, eliminating the break in the old capillary. If the break is at the head, you may have to unsolder the old tube from the head. In this case you will not be splicing, but inserting the new capillary at this point.
2. Use the tubing cutter to make all cuts. Follow up with the welding tip cleaner to gently ream the inside diameter of the old capillary to make sure it is open.

3. Clean the old capillary tube using the emory cloth for about an inch back from the cut.

4. Apply soldering flux about 1/8" back from the cut, so as not to make the solder flow into the capillary opening.

5. Fit the copper tubing splice over the old capillary; add a little more flux to the joint and solder. Check the joint for integrity and visually inspect to make sure the capillary did not get soldered shut.

6. Fill your small container with ice cubes, and add a small amount of water to create slurry. Add a tablespoon or so of salt to maintain as low a temperature as possible. The water slurry should completely immerse the bulb of the donor gauge.

7. Immerse the donor bulb in the cold water, and wait at least 5 minutes for the bulb to cool. This will keep the gas condensed in the bulb, and prevent it from escaping while you work with it open to the atmosphere.

8. With the bulb in the cold solution, you can now cut the donor capillary from the donor gauge using your tubing cutter.

9. Place the fittings from the old bulb, and the shrink tubing over the donor capillary and let them slide away from the joint. You don't want the shrink tubing to absorb any heat during the soldering process.

10. Prepare the donor capillary tube as you did the old gauge and tube using the emory cloth, and tip cleaners to make sure it is open, and prepare with flux. Remember, do not flux all the way to the tip of the tube. That will attract solder to the tip, and possibly close the tube, ruining the repair.

11. While the bulb is still in the cold solution, insert the donor capillary into the copper tube splice, add flux, and complete the solder joint.

12. When the joint cools, inspect for any flaws, or improper soldering. Re-do if necessary.

13. When cool, slide the shrink tubing over the splice, and heat gently to cover the splice.

14. Remove the bulb from the slurry.

At this point, the repair is complete. You can test your gauge, and make adjustments using a pot of water on the stove, and a thermometer. Small adjustments can be made by slightly bending the mechanism at the gauge head.

 

there was on article on the net about a repair kit for a mopar mechanical heat gauge. I read it a while ago and it was pretty easy to follow. I didn't like the idea of using either to replenish the fluid.