Help! Leaky Radiator Hose at Moto Meter Probe

[Erno730]

New to Model A's (am also all-thumbs). My '31 Roadster has a Boyce Moto Meter with a probe that inserts into the upper radiator hose.

I purchased a new upper hose, drilled a small hole, and inserted the probe casing from the inside of the hose. I then placed the outer metal plate over the probe casing threads and securely tightened the nut - the result was a leak around the probe insert.

Do I need to seal the probe housing cap in some way? Or should I switch to a more modern probe and instrument gauge? I love my old temp gauge but don't see a way to use this old probe with modern probe pipes or drilled water outlet necks. Any tips?

 

[Will N]

That's very cool. The probe is filled with a liquid with a low boiling point, like alcohol. When it heats up, the vapor pressure from the boiling liquid is sent up the tube (that's wrapped in wire to prevent it from kinking. It's very important that tube is never sharply bent or the gauge will no longer work) to a curved bourdon tube in the gauge itself. The vapor pressure straightens out the curve and that moves the needle in the dial.


If you have a leak around the probe, I wouldn't hesitate to use some permatex gasket sealer around the hole and under the plate.

 

[Big hammer]

I'am guessing! that your missing a washer on the inside the first piece on the probe. Looking at it installed the sheet metal piece has a washer that goes from the curved hose to a flat for the nut. Thinking you need a curved washer inside the hose to the probe flat. Only a guess! good luck stopping the leak

 

[Gary WA]

My connection is closer to the neck with no washers-No leaks for years- your hole in rad hose should be as small as possible to insert probe. The other is an unrestored one. again no washers.

 

[Synchro909]

I think a smear of silicone before assembly will seal it up.