Heating element liquid coverage and vapor temps?

[Captn Jack]

I have a 12 gal copper pot still I made and it uses a 3500W heating element. Is there something that I could put on the side that would let me know when the liquid is getting close to the element like maybe a thermometer tape etc? There should be a difference in temps from liquid to vapor right? I tried one of the heat guns and it didn't really show any difference in temps. Maybe I am completely wrong on this??