Which type of air filter uses metal wool in oil and filters dirt through capillary action?

• A. Paper
• B. Oiled Gauze
• C. Oil Bath
• D. Oil Foam

Answer: (C)

Metal-wool in oil air filters rely on an oily, capillary network. The metal wool is soaked in oil, creating many tiny capillary paths. As air flows through, oil is drawn into those pores by capillary action, forming a continuous oil film that traps dust particles. Particles adhere to the oil-coated fibers and are held back from entering the engine or space behind the filter. This approach differs from dry paper filtration, which blocks particles by size, and from gauze or foam filters that rely on different oil-impregnation schemes. The key idea is using a metal-wool oil bath where capillary action pulls oil into the structure to capture dirt.