All the oil filters have a bypass valve and once the filter media is plugged from those long drain intervals, the pressure differential opens that valve and unfiltered oil is what is lubricating your engine. That carbon black color in my drain oil is coming from somewhere and it darn sure doesn't look like it did when I put in the new oil. Use a white catch pan the next time you change your oil instead of the black one and then look at the crap that your oil filter is missing.
