Today's modern engines are designed to use light wide range visc.oils,I don't use such light oils in higher milage/older engines, depending on what vehi/time of year I'm changing oil I use 5w/30-10w/30 or 10w/40.
Common practice used by many, many people. Unfortunately with the tolerances these engines are built with, you cannot do that. What i mean is, if it were a situation where you had to lets say, add a quart, it probably wouldn't affect the engine, but the MDS system doesn't play nice with "common grade" oils.
I have no idea what doc's aim is here besides he loves any kind of attention. He has asked this question multiple times and has gotten the same answers.
