A reasonable request. For now I'll just explain that you're probably hooking up the crude oil to the ingredient input instead of the fuel input. Unfortunately, the game engine does not generate an "in arrow" at the fluid fuel input. The input and output arrows are only generated for the ingredient input/outputs. To hook up fuel, run your fluid fuel line up to either side that does not have an arrow.
If you accidentally loaded crude oil into the ingredient chamber, expect the furnace to output some solid fuel once you power it. The fluid ingredient input is an experimental feature I added to this furnace, and since this is a "furnace" prototype, the recipe is auto-selected, so it selects whatever recipe it can find with the fluid you put into it (in this case crude oil) based on the recipe's sorting order. For most oils this turns out to be solid fuel.
And yes, it does mean I tend to use these to make solid fuel in my games. :) Or as part of my rocket fuel chain.
