I have decided to use pennzoil in 2000 mazda protege.Now which grade to use here in toronto.The oil will be in there till end of june.Maybe I should mix in 1 liter of 10w30 dino or synthetic.I want to use regular dino juice.Why do bottles of oil have 946 ml.instead of a full liter,only castrol has 1 liter bottles?please help