Castrol "Full Syn" > Mobil 1 Full Syn because...

1) Costs less
2) Same base materials (just diff additives)

 

it's a common practice to break in your engine on mineral oil before switching to synthetic. it was recommended to me by my machine shop to do so when i had my engine rebuilt. i started with mineral and change oil at 100, 500, 1000 mile marks. after that i went mobil 1 full synthetic.

 

ok, news flash....

Mitsu breaks these motors in before they put them in the car. You think they build the motor, put it in the car, dump oil in and send it out? HELL NO

The rings and seats are almost fully sealed. The conventional oil thing is for rebuilds.....

All though, this is all opinion and speculation. Truth be known, it probably doesn't matter one way or the other. But the fact is, the motor is already broken in basically....so, if you are using conventional oil for that reason alone, no need to.