[77newell]

My 93 coach, and lots of diesels, has a vacuum gauge between the filter and the inlet to the turbo that shows you the peak vacuum achieved since it was reset. I keep an eye on it regularly, monitor my oil sample results and change the filter at least at the 4 year mark. This last one is because, with age and use, there could eventually be pinholes and I don't want to wait until silica shows up in the oil. Could the filter last longer? Yup, I've just gone with my comfort level and the proof I have at hand.