The more viscous oil may contain VM and base oils and else. Therefore such upgrade in viscosity grade can mean weaknesses, problems, less protection (and also mean reduced MOFT btw). Against the bingo lessons the insinuated upgrade can read like a clear downgrade and the funniest 1/8W-12.3456 can beat the 5W-50 in MOFT. This of course mazda3lover himself should do: start to read! Instead of watching bingo until MOFT is stripped of all meaning.