Using the information from oil which is a part of a technical system has been presented a couple of times. The results introduced so far usually dealt with wear metals which get into the oil. However, this paper is based on a different approach. We have assessed Anti-Oxidant and Anti-Wear Particles (AOWP) - oil quality is primarily determined by these particles. These particles are additives in the oil and their amount depends both on operating time and calendar time. In this paper we introduce some mathematical approaches used assess how the number of these particles affects residual useful life (RUL) and maintenance optimizing.