This is the fuel filter from our Duramax that I changed after 12,000 miles of use. I'm always surprised at how much black looking stuff the filter caught. You can see the contrast between the clean white inner filter and the dark outside media of the filter. They both start as the same color. I've always wondered if the black stuff is fuel contamination like dirt or what? I wish the filter mounted in the engine compartment, but it's underneath by the fuel tank, which makes it a crawl under job to change.