AzFireGuy - the reason is I am not sure the engineers have my best interest in mind in the design. They need the engine to outlast the PT warranty and get tremendous pressure to maximize fuel efficiency. I am just a guy trying to figure out if there is a trade off in fuel efficiency and protection with these thin oils. These thinner oil specs are a new phenomenon for a guy whose last newest vehicle was a 2008. If I can get better protection from a more traditional viscosity rated oil for 1/2 MPG I want to go that route. If that is total bunk, I would have nearly everyone jumping my case about questioning it. I think there is still a lot of debate out there and we may not get consensus until many millions of these cars get to high mileage- 200k plus- or fail prior - while running thin oils.