Anyone have any experience, or heard of people who did really extended drains in the 1960/70's? (ie., more than 5k miles on dino or 10k miles on synthetics). I just thought that with how much engines sludged up with poor maintenance or from poor oils in the 1960/70's, that most people got in the habit of 3k changes, and that became a sort of drilled-in norm. So when Mobile and Amsoil came out with 25,000 mile OCI's in the 1970's, it must have shocked a lot of people or been dismissed as a scam. Even QS recommended 15,000 mile changes with some of its 'Supreme' dino oils. Did anyone actually follow these recommendations and have success with them? I was just thinking a lot of people in general are still hesitant to run oils for long OCI's, so it must have seemed like absolute lunacy in the middle of the 'sludgy 70's'.