wvmarle:
Or a pressure sensor attached to the bottom - if you have a tap there, that's easy. Get a differential one that can handle the liquids & temperature.
does the volume of the fluid change with temperature ?
if it does, then your weight sensors would need to be calibrated for the elevated temperatures to display the correct volume.
if you are using something like a deep fryer, the food flakes and falls into the liquid, displacing fluids and altering the mass characteristics of the fluid, not by much, just point out that weight is an indirect measurement of volume.