I run MC 10w30 all of the time, but my dealer threw in MC 5w40 this last oil change for the same price because they were out of 10w30 HDEO. So far, the engine is quieter and I'm seeing fewer exhaust cleanings. I've always been a fan of the 10w30, but I might be rethinking it, especially since my wife noticed the quite engine and we're talking about a 2014 6.7 f250, not a 6.0. I'm really not seeing lower MPGs either, just a little quieter engine, can someone explain that?