Electrical energy plays an important role in Indonesia's economic development. In Indonesia, many islands other than Java, Bali, Madura, still depend on Diesel Engine as the source of electrical energy. Biodiesel as an alternative of diesel engine also makes diesel engine as one possible solution for producing electrical energy. In order to be able to use diesel engine in longer period, the maintenance of the machine is very crucial. This paper proposed the usage of information technology to create smart maintenance system for large scale diesel engine. Online monitoring is carried out to have actual observation of the running machine. The obtained data is analyzed to find the problems that can cause machine malfunction. Based on the problems, the system proposed recommendation action to be carried out by the operator, before it becomes catastrophic failure. The smart system consists of two main processes, which are data acquisition to have online monitoring, and the recommendation modul that has expert quality in solving diesel engine problems. The design of the smart online monitoring system is discussed in this paper.