The following is a fix for the bourdon tube type temp gauge ‘sender’ that has worked for me so far. I believe the most common fault with these is a break in the small pipe, usually where it goes into the tube which in turn lives in the intake manifold.
The first step is pretty straight forward. Unsolder the broken pipe, cut off the damaged section and re-solder the pipe the tube. The problem has always been –“How do you refill the system with ether and then seal it up?” Soldering won’t work because the ether in the bulb will expand with the heat as you solder an escape. Plus it is rather/very flammable!
What worked for me (so far) is to find a small brass machine screw and nut. Drill a hole in the end of the tube opposite where the pipe enters, large enough for the machine screw. Then solder on the brass nut. (Some tubes already have a re-useable tapered brass ‘plug’ pressed and soldered into a hole in the end). Fill the tube with ether. I used starting fluid. Spray a fair amount into a small container. Suck it up with a syringe and inject it into the tube. I found my gauge was accurate if I filled up the tube and then withdrew (I think) about 5-10 ccs. Too much starting fluid in the tube will cause the meter movement in the gauge to ‘pin’ and this is NOT GOOD for the tiny gear rack and spring assembly.
Finally wrap the small machine screw with teflon tape and teflon goop and screw it in tight. Wait for both to set. I tried various rubber washers first, but they all leaked under pressure. You can test the gauge for accuracy with some boiling water and a thermometer. Watch the movement carefully while testing for calibration.
One caution besides the obvious “don’t work with starting fluid around flames”. The problem is that the expansion characteristics are different for ether or whatever was originally in the system vs starting fluid – which is easily available.
Anyway for those who like a challenge, have some time, like to ‘putter along’ and are too cheap for the professional repair, this is another option.
1958 Mk1 Jaguar (from the Jag-lovers internet site)
(Submitted by John Fowler)