Each moving part and cylinder walls in the internal combustion engine require clean oil for proper lubrication and lasting life. Engine oil is intended not only to lubricate the rotating parts, but also to cool, clean, and seal the critical engine components. It also aids in suspending wear metals and hard particles such as soot that is produced in the combustion process. However, with engine operation, engine oil degrades. Carmakers usually recommend that car owners change oil on the basis of driving hours or driving distance. Engine oil filters may assist to delay the time of oil replacement. If used properly, a lube oil and filter combination can reduce wear and prolong the life of an engine and its components. Especially for this research buses used in regular long-distance routes were equipped with additional bypass oil filters. The oil drain period was extended to see the influence of additional oil filter on the engine oil and engine wear. Oil samples were taken periodically and sent to the laboratory. According to the results of chemical analysis of oil samples conclusions were made. An additional filter helps remove very small particles suspended in the engine oil, that is why the wear processes are reduced. An additional filter helps delay degrading of engine oil, so the oil change interval can be prolonged.