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.