Buster also talks about an Amsoil dealer who claims he drives 40,000 miles on one oil change. Who would even want to do something like that? Amsoil costs about 5-6 times what ordinary motor oil costs, so if somebody can go 3000 with ordinary motor oil you could go 15,000-18,000 miles with Amsoil for the same price (actually less, because you would be buying fewer oil filters). What is the point of risking the engine and going 40,000 miles except just for bragging rights? Who really cares? If somebody told me he had gone 50,000 miles on one oil change I would say, 'Who cares?' I think 90% of synthetic motor oil users would be happy with 15000-18000 miles.
I remember when Mobil 1 first came out they were saying that a person could go something like 25,000 miles on one oil change. Then they backed off from that. I get tired of any motor oil company that makes claims that you can go 25000-40000 miles on one oil change. Maybe you could do that with a tractor trailer truck being driven on the highway all the time with a lot of oil in the crankcase and with super quality filtering of air, fuel, and oil, and oil analysis. Locomotives can go a long way on one oil change but look at the amount of oil they carry, and the filtering, oil analysis, and add oil.
Sure, if with oil analysis the oil is still good at 40,000, why not. Eventually it gets kind of silly. Okay, you have gone one year and 25,000 miles. Why not go ahead and change the oil.