What do you all think of a 0W30 Heavy Duty oil as a year round fill? This oil is usually marketed as an 'Arctic' oil, does it mean that it's unsuitable for summer operation? I live in a climate that rarely exceeds 35°C and can remain at -30°C for weeks. Don't put too many miles on per year, mainly short trips with four or five long hauls a year. The engine is GM's 5.3 Vortec in a 4X4 app. Looking for good value, not the cheapest, year round fill. BTW the owners manual recommends a 0w30 for extreme conditions. It doesn't specify for or against year round operation. I have considered for this application: PC Duron XL, PC Arctic although it's not HD, Esso Superflo. I have yet to discover a supply of Castrol, Mobil in this grade. Current fill is Pennz. 5w30 Multi-Grade.