this is one of those stupid things where i am 99% sure i am right, but little nagging voice in my head makes me ask. i bought a tonne of oil from target, the havoline 64 cent/qt deal. they didnt have 10w30 or 10w40 which i use interchangably. i bought a tonne of 5w30's and a tonne of 20w50's. what i plan on doing is using 3 quarts of 5w30 and 1 quart of 20w50 for each oil change, this *^*should*^* net me approximatly a 9w35 correct? and this is ok to do!?