When you treat your engine with Microlon the first time, the Microlon resin is forced into the pore structure of the metal. When the micro-thin film has formed and no more resin can be squeezed into the surface of the metal, the rest of the Microlon resin will hang in suspension until your next oil change when it goes out with the waste oil. Additional treatments will not form a better film than the first one, so continually re-treating an engine is a waste of money.