F53 V10 Manifold Bolts

My Excursion had the V-10. I did the drivers side first. then a year later I did the passenger side. there is no pattern for the failure. I think its from the size of the hardware. the studs are just too small and the heat cycle weakens them and they break. another thing I noticed which I think contributes to it is that there is a shoulder on the stud which stops the stud. so the stud doesn't have anything positive to tighten against other than the shoulder so this lets the stud wobble around (albeit by a very micro amount) and over time it fatigues and breaks. because when you go to remove the broken pieces they will spin freely in the head. but when trying to remove them they stick at the threaded opening because the shoulder deformed the threads. If I was to do it again and had the time I would drill them out to the next larger size.

And yes, there is a reason the header bolts don't break. because the bolts have a positive stop and are torqued properly against all the threads.