i have two hyundais a 2003 sonata with a 2.7 v6.the oil cap says 5w30 recomended but manual says you can use 10/30 10/40.no mention of using synthetic oil. i have mobil 1 5w30 in it now.the 2009 santa fe has a 3.3 v6 in it the oil cap has 5/20 perfered.i have pp 5/20 in it.manual also states i can use 5w30 or 10/30.no mention of synthetics i would like to use one oil for both cars.do you think it would hurt to use 5/20 in both? i also want to use synthetics.asked a few mechnics at the dealers. some say use it and others say use dino.man am i confused help?