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DIY repair of a mechanical temperature gauge
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TOPIC: DIY repair of a mechanical temperature gauge

DIY repair of a mechanical temperature gauge 6 years ago #2245

  • YLG80
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REMARK 1: I don't make any business with the repair of any gauge or instrument. I just want to give you a tip to repair it by yourself.
So do not request me to repair your gauge. Thanks you.
However feel free to contact me if you need further information.
The bourdon tube between the sensor and the gauge has an external diameter of 2.00 mm with an internal diameter of 1.00mm.
It was coming from an old refrigator safety sensor.

I've tried to use the same method on another gauge with a very thin capillary tube to no avail.
The ether was freezing and plugging the tube preventing the ether to move back to the gauge bourdon reservoir.

REMARQUE 1: Je ne fais pas commerce de la réparation d'instruments de tableau de bord. Je donne simplement un truc pour le faire vous-même.
Donc ne me demandez pas si vous pouvez m'envoyer votre indicateur pour vous le réparer. Merci .
Par contre vous pouvez me contacter si vous avez besoin de plus d'information.

Le tuyau entre le capteur de culasse et l'instrument à un diamètre extérieur de 2.00mm et un diamètre intérieur de 1.00mm.
Il provenait du dispositif de sécurité d'un ancien réfrigérateur.
(dispositif de coupure gaz en cas d'extinction de flamme.)

J'ai tenté d'utiliser sans succès la même méthode sur un autre instrument doté d'un tube capillaire beaucoup plus fin.
L'éther faisait geler l'humidité ambiante ce qui bouchait le capillaire en empêchant l'éther de refluer vers le réservoir du mécanisme de bourdon dans l'indicateur.

Vintage Temperature Gauge repair.

Two years ago, I've removed the temperature gauge from my WWII Jeep Ford GPW in restoration.
The capillary tube was broken at the sensor bulb level screwed in the engine head.
This is an original painted can SW temperature gauge.


The bourdon tube (detailed picture)


I've decided to try to repair that gauge myself, but the first trials were unsuccessful.
At that time (during the winter when nothing else can be donne on the jeep), I've replaced the capillary tube
and resoldered the tube to the gauge and the sensor.

Easy task!

But refilling the sensor with ether was another challenging problem.
Despite of several different techniques, I was simply unable to inject ether into the circuit.(with a syringe)
Today, I'm still wondering how they were making that operation in mass production.
If someone has that information, please share it with us.
So I've temporary left that project aside while finishing my GPW restoration, with a repro gauge, but still trying to find the solution to that tricky problem.

Today, I've eventually found a surprisingly easy way to refill the gauge.

It uses what I would call "thermal pumping" or "thermosiphon".

This is an interesting method (and exciting for me) because this the application of a well known physical rule expressed in an equation : P * V = nR * T (Boyle & Mariotte)
(see wikipedia with a nice animated explanation : http://en.wikipedia.org/wiki/Boyle's_law

The gauge refill "thermal pumping" method is explained a pdf file.


Summary :

1- Ether is difficult to handle because it has a boiling temperature point of 35°C.
If you simply take a syringe filled up with ether in your hands (37°C), you will immediately see an ether jet coming out of the syringe.
The syringe will be empty in a matter of a few seconds.
2- Ether is a very good organic solvent, which does not help when in contact with plastic parts (syringe and piston gasket)
3- Ether is difficult to buy. Here in Belgium, you have to give your ID card and fill up papers if you want to buy it in a pharmacy.
Likely just to be sure that you don't buy it for sniffing !
4- Fortunately it's very easy to find a substitute for ether : a Start Pilot (or equivalent of other brand) spray used to ease the engine
start during the wither. It contains ether.

Thermal pumping

As explained above, the ether does really not want to be injected in the gauge circuit. The first obvious reason is the presence of air in the circuit.
In the document, I will explain a workaround to that issue using another spray commonly used by electricians (as I am) to debug breakdowns in electronic circuits.
This is called the "Super Cold" spray, or -51°C/52°C spray.
With that spray, the technician can quickly cool down a chip or a part of the circuit to track down thermal or intermittent breakdowns. That's a really efficient debugging method.
We will use that spray to quickly cool down the gauge bulb and the bourdon tube to pump the ether into the bulb, the capillary tube and the bourdon unit.
It takes less than a minute to complete the operation.

What you will need

- The gauge and its sensor. If the sensor is missing you could build up a new one with an brass tube. I give the original sensor dimensions.


- The gauge mechanism + bourdon unit should not be broken or modified. This would make it almost impossible the recalibrate.
- A capillary tube if you cannot afford to use the remaining length on your broken gauge. External diameter of a .078'' to .08 ‘’
A capillary tube can be found on eBay or in an old gas refrigerator, or in a old gas water boiler.
This the tube connecting the flame sensor to the safety valve that switches off the gas supply.
- Medical ether or a Start Pilot spray
- A Super Cold Spray -51°C spray used to debug electronic circuits. Such a spray can be found on Amazon for about 9.90 U.S. $


- A 100W-150W soldering iron to seal the circuit after refill (no flame for safety)
- A gas blow torch to resolder the capillary tube and sensor parts if necessary. You could also use your soldering iron.

For the complete method, please read the pdf attached.

File Attachment:

File Name: RepairTemperatureGauge-rev1-022014.pdf
File Size: 418 KB

File Attachment:

File Name: Reparation-ancienne-jauge-temperature-rev2-022014-FR.pdf
File Size: 746 KB

Contrary to what I’ve read elsewhere in this forum, you can repeat the process several times as long as you don’t modify the bourdon spring mechanism.
If you miss the refill, just remove and replace the sensor capillary termination used to refill the circuit and retry.

I hope that this method will help you with the repair of you valuable original gauge.
Please share you experience with us.

Last Edit: 2 years, 2 months ago by YLG80. Reason: Warning about capillary tube diameter

Re: DIY repair of a mechanical temperature gauge 6 years ago #2248

  • YLG80
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To complete the information on my repair method, I've checked the calibration of the repaired gauge against a °C thermometer and by calculation in °F.
Here are the results :


The accuracy is not good for low temperatures, but who cares providing that the accuracy is good in the useful range, between 60°C and 100°C.
(Take also into account the reading error on both instruments, one with a needle and the other with a red alcool index.)

I could not reach 100°C, but I believe that the reading would have been close to 212°F.

The following user(s) said Thank You: mathias1

Re: DIY repair of a mechanical temperature gauge 2 years, 9 months ago #2561

  • mathias1
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Hello Yves,

I've got a similar problem with a temperature gauge I bought new as a spare part. I did have an electrical shortcut which caused damage to the tube filled with ether.

Is there a possibility you can help me with the repair? Where are you located?


Re: DIY repair of a mechanical temperature gauge 2 years, 8 months ago #2562

  • YLG80
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I'm located in Belgium.
Could you post a picture of the damaged sensor ?
There is another post on a Temperature gauge repair using another similar technique:


Scroll down to mid of page to see how he did that.
Last Edit: 2 years, 8 months ago by YLG80.

Re: DIY repair of a mechanical temperature gauge 2 years, 8 months ago #2563

  • mathias1
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I uploaded the picture of the new one with the damaged pipe. The other picture is the old one.
I'm located in Antwerp.

Re: DIY repair of a mechanical temperature gauge 2 years, 8 months ago #2564

  • YLG80
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Thanks for the pictures.
On the second picture, I see the other end of the capillary tube.
Is that cable still attached to the engine ?
If yes, I suppose that the sensor is still screwed in the engine head. That would be good!

You should remove that sensor from the engine head and and keep its fitting+capillary tube+sheathing.
If you use the vehicle (what type is it? Tractor?) you can temporary plug the sensor hole with a standard plumbing fitting.

If your capillary tube is too short, I believe I've still have one on hand. But I've to measure the length.
Otherwise it's still possible to reconnect both ends with a bushing and solder it prior to refill the sensor with ether.
If you have all the parts you could send them to me in order to refill it.


Re: DIY repair of a mechanical temperature gauge 2 years, 8 months ago #2565

  • mathias1
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Hello Yves,

that would be great.
It's indeed a tractor.
I still have all parts, as it's a new one I fitted last year. First I was looking to buy a new one, but the supplier changed the design a little bit.
Can you send me your detail by PM?

Last Edit: 2 years, 8 months ago by mathias1.
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