The time is close for a change and I will be moving to 0W30, I drive short distances, mainly and in the winter even with 5W30 I get terrible milage. It may make no difference at all but I'm a littl nutty I guess - This is in a P/U with GM's 5.3L Should I use a 0W30 rated for gasoline engines SJ, often referred to as passenger car oil. (PC Arctic 0W30) Or A Heavy Duty Motor Oil designed for Diesel and 'some' gasoline engines? (PC Duron XL 0W30) BTW what is it that makes the difference between an API S and API C oil? Is it just better detergency and dispertion or is there a wear related component also?