I would think that if you blew a coolant hose, lost most or all of your coolant and kept driving, long enough to warp your heads, they got *damn hot*. I'm under the impression that any oil is going to sludge up and become gunk when they start experiencing insane temperatures like that. I doubt that Mobil 1 would have even stood a chance. I don't think it was the 9,000 miles that did it. Then again, I'm not nearly as experienced with this stuff as some of the other guys on here. So I'll let someone else chime in. I am, however, a very satisfied GTX High Mileage 5W-30/10W-30 user.