'34 dual gauge problem

[Ricosan]

I had my dual gauge (temperature/fuel) rebuilt and installed in my model 40 last week. When I picked it up from the shop, the temperature gauge wasn't showing any red color but I assumed it was because the engine was cold. On the drive back (about 20 miles)I could detect just a hint of red at the very bottom, not even up to the "cold" mark.

I took it back in yesterday and we took the sensor loose from the radiator hose and plunged it into a cup of very hot water. The red liquid in the glass tube came up about half way between the cold and the hot readings on the gauge.

We reassembled it. I took it out for a drive to warm it up and nothing! Not even a hint of red.

Any ideas as to what could be going on?