while it's obvious that a 0w/30 provides better flow and thus protection during the start up and initial drive phases than a 10/30, I was wondering about the follwing: if one compared a 0/30 and a 10w/30 with similar Cst numbers at 100c(212F), they have the same thicknes when the oil is warm..ok (for instance GC and Pennz.HM 10/30). But how about warmer start up tepms, in "mid" range? for instance, which oil would protect better during start-up and initial drive phase at tamps about 50-60F? would the 0w/30 be too "thin" for summer starts? would a 10w be better for a motor during the summer for start-up, UNTIL oil reaches its highest visc? in other words: would the very good cold-flow capacities(low visc. at low tepms) of a 0w-30 be a DISadvantage during start-up at HIGH temps, cause its thinner than it "needs" to be at start-up? (sorry if this point is stupid..just wondering) Thanks for any educating answers.