Hello all... my wifes accord takes 4.5 qts of 5-20 and my canyon takes 6qts of 5-30. My truck usually gets changed every other time the car does as my wife is always going going etc... My question is would it be ok to save the half quarts left from my wifes car and use it as the 6th.qt for my truck? I buy the 5qt jugs of qs synthetic for 19 bucks and buying an individual qt is like over $6 alone. Thanks in advance