Abstract: To control the viscosity of oil circulating in a forced-oil circulation path of an engine, oil is conducted to a receptacle located, for example, within the oil pan of the engine or in communication with the overflow outlet stub (14) of the oil pump (3), and oil is conducted from this intermediate receptacle, for example in form of a pan (6) in two parallel paths. One of the paths conducts the oil directly to the suction inlet of the pump after, however, having to overcome a static pressure, for example by flowing over an elevated weir, notch, or through an overpressure valve; the other path is through a flow resistance element (7), for example a constricted tube, a lamella package, or the like, and then to the cooling portion of the oil pan, remote from the suction inlet of the pump.