High load equipment is well-worn by the end of the operating period, though, following the instructions and normative operating periods it is still repaired, going through relatively high costs to maintain its operational condition. The methods of engineering diagnostics here are ineffective because they are supposed to be used under the conditions in which equipment hasn’t exhausted its service life. That’s why the development of economically proven method of determining the service time of opencast automobile transport and other high load equipment is up-to-date. The choice of the efficiency criterion is very important. Average general expenses for equipment constitute this criterion; they include its purchase and all operational expenses, including maintenance. The article describes mathematical model of optimum operating period of high load equipment. Optimum operating period is determined when solving the problem of minimizing average expenses for purchase, exploitation and maintenance of the equipment according to statistic data. The realization of the suggested methods at the enterprise will make it possible to reduce expenses.