Abstract: A system is provided for regulating the oil temperature of a diesel engine while the latter is in various operating modes. The engine includes a heat exchange unit through which a heat exchange medium circulates and while the engine is in certain operating modes, the system directs the oil flow through the heat exchange unit so that the oil is either heated or cooled by the circulating heat exchange medium. The system includes a valve housing provided with a cavity having an oil inlet port, first oil outlet ports connected to the heat exchange unit, and a second oil outlet port connected to a passage for bypassing the unit. Disposed within the cavity is an adjustable element for effecting interconnection between the inlet port and a selected outlet port. Adjustment of the valve element within the cavity is determined by the oil temperature during predetermined operating modes of the engine.