Doesn't screw them up? Are we talking a fuel injected motor? I'm clueless here but that seems scary to me. I have a 2005 silverado. I can just see the motor smoking like crazy and blowing up or something and having to tell the dealorship that I ran premix in it . That's when they look at me like I'm stupid.
Been doing it for five years, 60k miles on my Ranger. 2.2l FI engine.