What is the operating temperature of glycerine?

Boshart liquid filled gauges are filled with 100% (99.7% min.) glycerine, which starts to become viscous at +17°C. As the temperature decreases, the more viscous glycerine becomes, causing the pointer to move slower to its correct position. It can even take several minutes.

At -5°C these gauges no longer operate. For operating temperatures less than -5°C, glycerine is mixed 2 parts glycerine with 1 part water (66.7% mix). This actually lowers the freezing point of the solution allowing the gauge to be used in temperatures as low as -46 °C. This 66.7% glycerine mix is available for such applications.