Is the concensus of this forum that 0W-30 will have a measurable affect on mileage? My application is a '01 GM 5.3L 4X4. As far as brands, I am debating between Mobil 1 and Amsoil. I have used Mobil 1 in the past and noticed an increase in oil consumption. Could I expect this with Amsoil as well? The truck in question has not had synthetic in it and is currently using Castrol Syntec Blend 10W-30. I'm a little leary of 0W-30 oil and leaning towards the 10W-30.