I Attempted to Repair a Mechanical Temperature Gauge - It Does Something Weird Now, Why?

[DB26]

Hello everyone,

 

I recently bought an inexpensive, broken mechanical temperature gauge from the teens or twenties. I attempted a repair on it today, but it didn’t work quite as well as I had hoped. Here’s what it does:

 

 

I put the new soldered-on temperature probe into some boiling water and the needle immediately responds, but only goes to about 140 degree and then immediately falls back to 100. What would cause it to do this?

[ply33]

Thought 1: Do you smell any ether? Could be a leaky Bourdon tube the leaks more when it unwinds under pressure.

Thought 2: There is a mechanical linkage between the Bourdon tube and the needle. Maybe it is bent/broken so the unwinding of the Bourdon tube is not moving the needle properly.

 

Just guesses, though.

[trini]

The sending unit at the end of the thin long copper tube  which is inserted into the water jacket in  the head is filled with a special liquid and sealed ( leak proof ). When heated the liquid expands and goes into that curved piece of gizmo in the clock which then tries to straighten  out and move the needle upwards. Most likely the gas in the bulb is leaked out. It is impossible to do a home fix on these mechanical gauges.

There are folks out there who do such repairs. Moss Motors in California will be able to connect  you to   their repairers who do the Lucas brand.  They all work on the same principle. Cheers and good luck mate.

[DB26]

Thanks both of you. I don’t smell any either. I will have to investigate further into the mechanism. And trini, thanks for your thoughts. I have seen a few websites that say you can do a home repair of these mechanical gauges. The trick is submerging the bulb in salted ice water and being quick with the solder repair. That’s what I did to this gauge, as there was no bulb or most of the capillary tube present when I began. All I had was a nub to work with. The gauges’ needle moving at all is kind of a win for me.