What is the main difference between a dry air filter and a viscous air filter?

• A. The viscous air filter is wet and typically oil-coated
• B. The viscous air filter is dry
• C. The dry air filter uses oil
• D. The dry air filter is not used in engines

Answer: (A)

The key difference is whether oil coats the filter media. A viscous filter uses a layer of oil, making the surface wet and sticky so dust particles are trapped by the oil film as air passes through. A dry filter, by contrast, relies on the porosity and structure of the filter media itself and has no oil coating, so it remains dry. Because of that, the description that the viscous filter is wet and typically oil-coated correctly captures its defining trait. The other statements conflict with how dry filters operate (no oil) and with the fact that dry filters are indeed used in engines.