I've been inspecting and changing my vehicle air filters for decades. The paper element used to get visually dirty within reasonable amount of driving, but over past ten or more years they appear to stay clean far longer. Way past 30,000 miles. I inspect by holding up to sun or strong light bulb and looking through filter paper. Is this longevity due to simply cleaner roads, environment? I don't think the filter paper has gotten more porous has it? Another thought is that many newer vehicles have air intake tunnels leading exterior air into the filter box, whereas older vehicle has filter box right in engine compartment, where perhaps road dust become more concentrated and so was more drawn into the filter. Anyone read any study on this topic?

Hi. I noticed this to. Many cars are now taking the air from the inner fender-wells which are not expossed to the open road.

I take out the filter and bang it on a white piece of cardboard. If a lot of fine particles come out of it I replace it with one I keep in stock.

Good luck!