Oil filtration unit for removal of contaminants from oil including a housing with an inlet to receive contaminated oil from surroundings and release oil to an inner opening at a first pressure, an outlet adapted to release filtered oil to surroundings, and an oil filter for filtering oil in the inner opening of the housing. The oil filter includes an inlet with an outer surface, an inner volume to receive filtered oil at a second pressure lower than the first pressure, and an outlet inside the housing providing fluid/liquid communication between the inner volume and the housing outlet. The filter outlet includes a hydraulic resistance providing a fluid/liquid flow restriction between the inner volume and the housing outlet to increase the second pressure inside the inner filter volume and release the oil from the inner filter volume to the housing outlet at a third pressure lower than the second pressure.