I’m torn on this whole debate, I’ve only run 5,000 mile oil changes for the last 10 years on synthetic, and prior to that it was 3,000 miles on conventional. I did deviate from that slightly for a short time, and went running 7,500-8,000 mile intervals for a year or so on my Lexus LS460. And then I experienced oil consumption. Everything was going just great until I decided to try THAT, BUT this also coincided with a higher mileage point. No oil usage before 100,000 miles. Then it increased a little bit at 115,000, more at 125,000, until finally it was drinking a quart every 1,000 miles at around the 150,000 mile mark. Did “extended“ drains do THAT? I don’t know, I’m not sure. Maybe it would have happened regardless? I will say that I drove a car to 289,000 miles doing only 3,000 mile intervals with conventional 5w30 and at 289,000 miles that thing started drinking oil too (1 quart every 1,000 miles). No extended drains, ever. Still the motor was guzzling oil and stalling at 289,000 miles. My shorter intervals didn’t prevent that, and then half the car was rotted out anyway.
I guess my point is, I’m going to try extended drains using a certified oil that meets my vehicle’s requirements. I own a Toyota that recommends 10,000 OCI’s. I have never done that, I’ve always done 5,000 miles. I’m going to go the 10,000 miles and try it. Worst that can happen is my car is rusted out at 200,000 miles and consuming a lot of oil. Either way I don’t think doing twice as many oil changes is going to change much of any of that. So here I go...10,000 miles here I come.