straight 30 in my 49 3600, but i have ran 10w30 synthetic Mobil 1 in my 1994 chevy truck (since brand new in 94) it has a 350 v8 and 196,000 miles without a single problem, it starts easy weather its 105*, or -5* degrees and doesn't burn or use oil, runs great and has survived 2 teenage drivers- so it was driven hard, so Mobil 1 has my vote
