Conditions of the elements of tribomechanical system are very complex and determinate great deal by the adequate characteristics of lubricants. Complexity of conditions is determinated by: temperature of elements in contact and temperature of lubricant, outer load (specific pressure in contact zone), dynamic character of making contact and power and motion transmission. In regard with primary role of lubricant to reduce the negative effects of tribological processes related to friction, wear and increase of temperature in the tribomehanical systems, all types of maintenance include lubrication as a very important part of the whole procedure. On the other hand, lubricant is, as the contact element of the system, carrier of information about the state of the whole system, from the aspect of tribological and other ageing processes. Due to that, analysis of oils, based on properly defined program, represents a very effective metod for monitoring the state of tehnical systems, which ensures early warning signals of potential problems that could lead to failure and break down of the tehnical systems. In the systems structure, besides the mechanical components, the state is also changed of the lubricant itself, what leads to loss of lubricating properties. Investigation procedure of physico-chemical and tribological characteristics of lubricant during exploitation consists of following: oil sampling from real tribomechanical system; measuring physico-chemical characteristics of oil; establishing of wear products participation in oil and measuring tribological characteristics of tribomechanical system in model conditions using sampled oil as lubricant. Analysis of oil samples which contain particles, created as results of wear, enable evaluation of system tribology condition in different phases of system exploatation. In this project, it will be presented results of experimental research physico-chemical and tribological characteristics oil was sampled from engines of vehicles, Mercedes O 345, that were exploited. The research was conducted through periodic sampling oil from engine vehicles listed above. Apart from the fresh oil (,,zero" sample), samples are taken after 10.000 km, 20.000 km and 30.000 km. During the sampling of oil choice of the sampling were conducted carefully according to the actual oil usage, which enabled each sample as representative one.

The central component of the tribomechanical system is the lubricant, whose most significant function is the lowering of friction and wear appearing in the contact of two surfaces in relative motion. As a subsystem, tribomechanical systems are integrated everywhere into the technical systems. Apart from more significant applications in internal combustion engines, transmission, and hydraulic systems, there is also a large number of further applications. Due to the poor execution of the tribomechanical system or inadequate application, if it is not fit for the given system, commercial losses may occur measured in billions of euros annually. That is why the significance of the tribosystems is not only technical, but also economic and environmental. The concept of the future successful development endeavors to associate economy and ecology into a complex and noncontradictory system. AE