Is there anyone source that changing oil every 3000 miles came from or is this just advertising? The reason I ask is that no car I have ever owned has stated this length. My current car 3750 miles severe/7500 normal. My previous was every 6000 miles and prior the same. Was this an old school thought due some other work needing to be done back in the days of points or carb. adjustments etc that made sense. My current mechanic who is really good uses 3k with dino which I ignore till 5k. My previous mechanic stated 5k miles was fine (by sticker) but was a European concentric shop (specialized on Porshe, Audi/VW, Mercedes, BMW etc) but worked on my lowly but reliable Honda. Just a random ponder as some people are fanatics about 3000 miles which is fine.