Should have a fuel tank, and must be able to run on diesel OR oil. It has to work with both. it has to have an exhaust, and on/off buttons. It needs a fuel gague, and an indicator to tell [the player] that the fuel has run out.
Place a design in here, so we may tell you what should be improved.
Here's two designs if you require a model:
The first one has pretty much the same concept as an engine. Use something to burn something and create energy.
ehm yeah... i should make one