And I can't tell a bit of difference over the ACD. But why would I expect to with such a small difference in viscosity. However, there is an interesting change in how it flows down the head. With the ACD, it was a steady smooth flow around one of the headbolts. It was hard to tell it was actually flowing. I've observed this many times and I took one last look since this is the first time I've tried a different oil since going with ACD since the car was new. The Redline had a narrower flow path yet it was deeper. I could see the flow easier because it would alternate from flowing around the bolt to taking a differnt path 3/8" away from the bolt. Very weird since flowing away from the bolt was not the easiest way down. I've heard this before, but can anyone confirm the 10w-30 is actually a straight weight oil as in VII free?