I've just found an unexplainable sediments at the bottom of the oil drum contains engine oil. There's not much time passed from production date and the oil was fresh. For inspection i took 2 samples and tested every parameters which can assure us to reach a solution and explanation for the settled black layer. The samples have been taken from upper oil of the drum and also from the bottom. No deviations have found in the test results. Has anyone experienced such case so far? If yes, does this affect the oil shelf life? or will it cause an operation failure?