I'm someone else who burns used motor oil and tried Amsoil once. A couple quarts in my '01 HO it did fine, no blue smoke or anything, but my '03 didn't like it as well. . . it did make blue smoke at light loads.
Haven't tried it on my '96. I have 3 quarts of Rotella synthetic in the '82 Blazer diesel I'm driving right now (backup vehicle) and it burns fine. I have quite a concoction in it right now: 7 gallons WVO, 1 gallon old motor oil (mix of Delo 400 & Rotella syn), I gallon of mineral oil (from a transformer), 1 gallon gasoline to thin it out a bit, and an extra dose of Amalgamated fuel additive. So far burning it real well. Tank is about 30 gal so this makes about 30%.
Vaughn