I've used Original GM 5w30 synthetic Dexos1 (made by Cosan that makes also Mobil 1 in here, so I figure if this is M1 actually) in my cars. My Subaru with 122k miles doesn't like any 5w30 anymore, or I don't like the way it sounds with any 5w30 when at op temps. In the Taurus, is fine, no weird sounds at all (good old Vulcan). I'm still on GM Leget in the Taurus, it just uses a little more oil than with M1 15w50 at road speeds, because of the lower viscosity (they are both M1 syn in my opinion, but Cosan didn't answered my question if they are the same oil for cost production reasons). City driving isn't giving greater consumption, just at highway long trips (470 miles straight).