Speaking of cleanliness...I was speaking with a Diesel engine machanic, and his spoke well of synthetics. He generally said around 1,000,000 miles semi engines would come in for overhaul. He said regardless of synthetic at 30,000 OCI or dino at 12,000-15,000 OCI the engines were usually in need of some work (go figure at 1 mil). However, he said the engines using synthetic were always much much cleaner, almost to the extent of being able to wipe it off with some glass cleaner and serve dinner. I had a caddy engine massively overheat at idle at shut itself off, but I feel Mobil-1 10W-30 was its saving grace as to not seize. It started up and kept going. My brother-in-law's farm tractor was operating a grain elevator via PTO, so nobody was in the cab. A hose broke and it overheated so badly, it stopped. It had Conklin(sp) synthetic in it. He said they fixed the leak, topped off with a/f and it started and ran fine. Maybe a dino oil would do this, also, but I doubt nearly as well. So, not only are there extended drain intervals, but cleaner engines, high temp protection, superior low temp flow, a chemical bond that will keep an oil film on metal parts for less 'dry starting', less or no viscosity loss, better shear stability, better protection in warm/hot climates and the list can go on. Is Amsoil superior?..to most oils yes, but to M1, GC, RL, etc, most likely not. And I would NOT recommend doing their 25000-35000 OCI!! In fact, I believe there was a test done with Amsoil and M1 a while back in the UOA section, where equal usage, filter changes and driving was done, with the oil being tested at every filter change/top off. I think M1 outperformed Amsoil by a long shot, with TBN, etc!!