How do you make a decision on which oil to use first? I have the oldest I bought was Valvoline Advance Maxlife Synthetic and still have 1 5qt with a partial one with 4 qts all are March 20 then I recently bought Shell Gas Truck 0w20 jugs (3), 6 qts 0w20 , 5 qts 5w20, and 3 qts 5w30 on cheap oldest being January 19. Vehicle takes 6 qts with oil change averaging 9 months. Thought about using partial 5w20 Maxlife and 2 qts Shell first but don't know if base would be affected since different companies as well as different specifications SN+ and Sp. All oils meet certification requirements although manual states 5w20 or 5w30.