Naval Maintenance and Mechanical Tools – Technical Manuals, Fasteners, and System Operations Practice Test

The test checks how much water and solid debris are present in lubricating oil by separating the immiscible water and sediment from the oil. In a BS&W (Bottom Sediment and Water) test, the sample is spun or allowed to settle so the water and any sediment drop to the bottom, and the volume or weight of that bottom layer is measured and reported. This directly indicates contamination levels from water and particulates, which can harm lubrication, cause corrosion, or clog filters. A higher BS&W value means more contamination and usually prompts oil replacement or filtration steps.

Viscosity, flash point, and specific gravity tests don’t measure water or solid contaminants in the oil. Viscosity looks at flow resistance, flash point gauges flammability risk, and specific gravity compares density, none of which directly quantify contaminants.