I believe the factory recommends 5-30w, what I've always done on my daily drivers and summer toys is after the first 500-750 miles change the oil with the high quality oil of your choice, not synthetic, run another 750 to 1000 miles any swap to synthetic, I like Mobil one but Royal Purple, Red line and a host of others offer quality synthetics. If you building a high performance motor, add another 2 oil changes, one after the first 10 minutes of run in, and another at the 50-100 mile range, again do not break in a motor with synthetics. This procedure has served me well from a 4 cylinder, 120hp Ranger to a 800hp Chevelle, I have yet to toss a motor.