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how did you seal the wire with spring in the connector?

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I am not sure but you may be missing a part.
I have attached photos of mine, as my motor is away at the machine shop it is easy to shot the temperature sender unit.
The top picture is the sensor, it looks like this is what you have threaded into your motor. Note that the 'spring' is actually only a coil put there to stop the hollow tube inside from being kinked and not allowing the mercury inside to reach your display on your instrument gauge and give an accurate reading.
The middle picture is what you may be missing. This fitting threads into the head first. It is a pipe thread so the external threads are tapered to seal as they are tightened into the head.
The bottom picture shows how it looks when assembled. The square nut on the sensor assembly threads into the fitting in the head
The sensor actually seals to the inside of the fitting keeping the coolant from leaking out.
The coil and centre tube are sealed independently to the sensor, and the nut that holds the sensor into the fitting is actually square so that the threads are not continuous so it is only the sensor's fit into the fitting that completes the seal.
You can use Teflon tape on the pipe threads to improve the seal of the fitting to the head if you have a leak around the fitting due to nicks or chips in its threads.
Clean and polish the sensor and the inside of the fitting so dirt and impurities do not cause an improper seating of the two and allow a leak.
Hope this makes sense.
Bob J.

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hi bob,

Thank you. I'll disassemble it and see what's missing. hello mike

Actually, the tube and line are filled with ether. Mercury boils at around 670 degrees F. I carefully removed a temp gauge line from a 1937 Chevy decades ago. Once out, I attempted to straighten the line and ended up cracking it. The smell of ether is strong!

I know this is an old thread, but my temperature gauge isn’t working and I just installed an aftermarket (and temporary) temperature gauge.

On my car the square head “nut” is in fact the fitting.

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Its pretty common the gas/fluid/whatever in that tube to developed a leak. You'll have to send the entire assemble (bulb, tube, gauge) out to be serviced and calibrated.

Hey Don,
You're lucky to get that fitting out of the head. Mine was so siezed I had to drill it out just under the thread size and re tap it. As for the gauge there is a gentleman by the name of Roy Martin who did repair them in the past - not sure if he still does. Others on the site will probably have more current info. He was very reasonable with quick turnaround and my temp gauge has worked flawwlesly since he reconditioned it. His address is:
Roy Martin,
172 Laurel Hill Dr.,
South Burlington, VT. 05403

The only email I have is Roymart@comcast.net - don't know if it is current. Nice to have your original dash gauge working. And if your head is the same as my '39 the hole is 5/8-18 NF
Hope that is of some help. Chris.

Thanks for the information. I’m very fortunate that the car was really well cared for for all the years it sat. It was always in the garage and kept clean.

As a result, I’ve had a lot of things go easier than what I’ve seen for others.

I had the entire system overhauled by Kaja Tachodienst in Germany. top quality

Thanks, Mike.