Obviously we have two different uses being discussed here, gasoline and diesel. Using the same oil, a good universal 15-40 diesel rated oil, when it is used in my gasoline cars it is good as new after 7500 miles, but when used in my diesel I change it every 3500, along with the filter because about that point the level starts to drop, i.e., I have to add more oil. The oil seems to wear out with use. It is being constantly polluted with more and more carbon each day, and the filter certainly doesn't take it out (being sub-micron), perhaps there is a displacement thing going on here. Does anyone else notice the "wear out factor" in relation to diesel use?

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