But is that really true? It turns out that filters, especially those used for air and fuel, can in fact suffer from being replaced too often. Indeed, as difficult as that concept may be to believe, most filters are least efficient when they're new. As a filter begins to capture contaminants, its ability to capture more contaminants increases. The bits of belt dust and acoustic insulation that become lodged in paper air-filter elements, for instance, improve the paper's ability to capture new debris and contaminants as they pass through the filter media. And the same is true for fuel filters: As they begin to capture the first bits of asphaltene (a common diesel contaminant), rubber hose particles, and rust from steel tanks, they become more efficient at capturing still more of this and other contaminants.