I've experienced two engines with failed rod bearings, one a V8 and the other a 4 cylinder. Both sounded like that. Not saying it couldn't be something else, but the sound is consistent with a rod bearing. When cold, the oil is somewhat thicker and pressure is higher. Above 1500 RPM pressure would also be higher than at idle when warm. That may be enough to float the journal and prevent knock. I would switch back to Mobil 1 and maybe bump the viscosity up slightly and see if the knock goes away. That should give you a good idea if it's a bearing. Good luck!
07:54:19 09/17/10
