If put in contact with metals, especially copper, zinc and silver, it will greedily take on new ions. It will, literally, remove metal from the inside of your boiler, and leach the silver right out of the solder joints. In very short order it will make your boiler safe only for use as a doorstop. Steam oil is a substance concocted especially to lubricated the internal moving parts of steam engines. Animal and plant based oils break down under heat and pressure.
Mineral based oils break down in the presence of water.
Neither alone is suitable in the environment of a steam engine. Steam oil is what is called a compound oil. It is a combination of both animal and mineral oils together, with stabilizers. Treat each part of a machinist's kit as if it were the entire project. Take on the project one piece at a time.