haven't tried this myself, but this is how it's done. Nissongers in NY
reportedly does the whole guage for around $100.
Dave
from: http://www.ply33.com/Repair/TempGauge.html
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 serveral 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 suppy, 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 212° 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 termperature
by placing it in boiling water (212°F) then bending the linkage that
connectes the Bourdon tube to the indicator. Do not bend the Bourdon
tube itself.
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.
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 awayfrom 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.
In general I don't make commercial endorsements on this web site. But I
have to say if you repair or restore old cars a subscription to Skinned
Knuckles is required.
Copyright © 1999, 2000, by Tod Fitch
=====
They can kill you, but the legalities of eating you are quite a bit dicier.
David Foster Wallace
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