I have the same concern on multiple oils. I would like to use one oil in all my rigs. I buy a used car with Castrol useage, and I have used Vavoline. I heard Valvoline was superior, then I hear other heresay. I would like to see some oil test results which show the comparisons of these two oils,pour,flash, etc...which to me as a novice don't mean much. Is the real fact, that if you change your oil every 3000 miles it doesn't matter what oil you use...castrol,Valvoline, Mobil, Amsoil or...