Thermal and hydrodynamic concepts are of a vital importance; therefore their assessments are unavoidable for the purpose of hydraulic systems. The present study implements the practical updated knowledge of the expertise for both of the hydraulic and thermal fields in an expert system model. This is implemented in order to improve the performance of hydraulic system by considering the thermal effect on the hydraulic system operation. Accordingly, a computer program (Hydraulic System Calculations), designated as (HSC) implements a Visual Basic language in the Microsoft Visual Studio 2010 software has been built. Regardless of the design requirements, the code is capable to deal with (18) possible connection types of the actuators, in series or parallel, arrangements. The suggested code provides the designer with a number of choices, different kind of connections, to resolve the problem of hydraulic oil overheating which may arise during the continuous operation of the hydraulic unit. As a result, the (HSC) is able to minimize the human errors, effort, time and cost of hydraulic machine design.