Broken Temperature Gauge

 Disclaimer: While an effort has been made to assure a reasonable repair procedure, no
 guarantees are made. We are not responsible for any damage or injuries that may occur as a
 result of following these instructions. The only vehicle these procedures has been tried on is a
 1933 Plymouth PD. Applicability to any other vehicle is for you to decide. 

 The temperature gauge is a "mechanical" unit. It consists of a bulb with fluid (ether) mounted in
 engine head, a gauge head mounted in the instrument cluster on the dash, and a tube
 connecting the bulb to the gauge head. The gauge head is actually a pressure sensing unit. 

 In operation, the heat of the coolant in the engine head heats the working fluid. As
 the engine gets hotter the pressure in the bulb and tubing rises. The dash head
 unit simply reads the pressure on a scale calibrated in degrees Fahrenheit. 

 A common failure mode is for corrosion to lock the bulb in the engine head.
 The tubing is twisted off near the bulb when bulb removal is attempted. In this
 case, the gauge head unit is known to be working properly, the defect is in the
 tubing and in the loss of fluid from the sealed system. 

 Replacement parts

 Mechanical temperature gauges are still being manufactured and available in most auto parts stores.
 The goal of this procedure is to graft a new bulb (with fluid) and tube onto the old gauge head. 

 Find a gauge that has a spiral wound protective cover over the tube. There are some that use
 a plastic coating. While these can be made to work, they will not look correct. 

 The Procedure

  1.Carefully remove the old tubing from the gauge head. On my unit, the tubing was soldered into the
      gauge head and then the spiral protective wire wrap was crimped. Gently work the crimp loose
      then unsolder the old tubing. A relatively high wattage electronics soldering iron works well. An
      inexpensive, low wattage, iron from the local discount electronic store did not work for me. 

      Caution: The working fluid in the gauge is ether, a highly flammable substance. Do
      not have any open flame near your work area. Do not use a torch for the soldering
      operations. 
  2.Tin the opening where tubing goes into the gauge head unit. Do not fill the hole with solder. The
      gauge will not register without a opening between the tube and the gauge. You want to handle the
      gauge head unit as gently as possible. I feel it is better to use a high wattage iron to clean up and
      tin the gauge head before the heat is propagated to the whole unit. 
  3.Measure the tubing length on the old unit. Mark off that same length on the new gauge's tubing.
      Measure from the bulb. The distance is not real critical and all after market units I have seen have
      a very generous tube length. If you end up a bit long you can coil up the excess under the dash. 
  4.In a container several inches in diameter and several inches high, bury the sensing bulb in a
      mixture of crushed ice and salt. This will cool the working fluid enough that little or none will
      escape. You will keep the bulb in the ice until you have finished all cutting and soldering,
      so be sure the container will not fall over or the bulb cannot accidently be pulled out. 
  5.On the gauge you purchased at the local auto supply, trim off the spiral protective wire wrapping
      for about 3/4 of an inch around where you will cut the tubing. Do not cut the tube yet. 
  6.Tin the exposed new gauge tubing using standard electrical solder and your soldering iron. 
  7.Make sure that the sensing bulb is still in the ice and is cold. 
  8.Keeping the sensing bulb packed in the ice, now cut the tubing just slightly closer to the head unit
      than you measured earlier. Once cut you can slip a the bolt cutting portion of your electrical
      crimping tool over the tube and re-cut it at the measured position. The reason for re-cutting the
      tube is to assure a clean round opening, the first cut is likely to have collapsed the tubing slightly. 
  9.Keeping the sensing bulb in the ice, slide the tinned section of tube into the tinned opening in the
      gauge head. Solder the tube to the gauge head. Any voids are likely to be leaks and any leaks will
      cause the unit to immediately fail. On the other hand, if you end up sealing the hole between the
      tube and the gauge head the unit will not register. 
 10.After visually verifying that a good solder joint with no voids or other defects exists, you can
      remove the sensing bulb from the ice. You will want to completely rinse the bulb in water to
      remove all traces of the salt. 
 11.Place the bulb in hot or boiling water to test it. The gauge should now be restored to operation. 

 Calibration

 If the gauge does not read 212ø F in boiling water you have two options: 

  1.Note the error and live with it. 
  2.Attempt to adjust the gauge head unit. 

 The gauge head is a Bourdon tube connected to the indicator by a linkage. The Bourdon tube is simply
 a flattened tube rolled into a coil. As pressure is applied the tube slightly unwinds. When the pressure
 is removed, the coiled tube returns to its original position. 

 Adjustment is made by bringing the sensing bulb to a known temperature by placing it in boiling
 water (212øF) then bending the linkage that connects the Bourdon tube to the indicator. Do
 not bend the Bourdon tube itself. [Chrysler 1953 page 70] States that it is possible to
 adjust the gauge if its reading is less than 30ø different than the actual temperature. 

 If you have any doubts about the adjustment operation, then don't do it. You can
 buy replacement sensing bulbs and tubes at any auto supply store. Getting an
 original gauge dash head is a lot harder. 

 Installation

 Avoid sharp bends or kinking the tubing when installing the repaired gauge. 

 Update

 In the April 2000 issue of Skinned Knuckles magazine there is an article by Bill Cannon on doing this same
 repair. A significant improvement is given by Bill in splicing the old tubing on to the new tubing with the use of a
 sleeve. This allows you to work away from the gauge head and thus be less likely to damage it. 

 In the Restoration Forum of the June 2000 issue of Skinned Knuckles A. R. "Dick" Evans ("The
 Temperature Gauge Guy") of Dunedin, Florida pointed out the safety issue of working with an open
 flame near the ether working fluid.