The key point here is that, ALL physical properties for the new fluid must be defined in the database. If any rows are left as "undefined" the fluid won't be available to model in a system as all properties must be defined.
Let's consider the fluid below. In this example, Diesel has been added to the fluids database however, the user hasn't entered data for viscosity. As we can see, viscosity is "undefined". This means this fluid won't be available to you if you attempt to assign the fluid to a model from a Known Pressure, Reservoir or Known Flow Boundary node.
If however you complete the data-entry by defining in this case, the viscosity, the liquid light-bulb is then illuminated and the fluid will then be available to you if you attempt to assign the fluid to a model from a Known Pressure, Reservoir or Known Flow Boundary node.
