Originally Posted by cbdallas
There's a few too many manufacturers putting in M1 5W-30 at the factory for me to believe that it's shearing to the point of engine damage. While I don't dispute that it shears, I do dispute that it's killed any engines.
If you know something breaks down prematurely, why run the risk? Do you also take expired medication? Some engines are more sensitive to it than others, like a flat four, but the Subaru forums have noted many cases of spun bearings with cars on Mobil1 5w30 and the oil analyses to prove it. The ST is still unknown territory, but why not try something that has been proven both on and off the track. Plenty of data shows it holds up well. Some people just get very defensive when new-to-them information surfaces.