Took the Sonata for the first free dealership oil change (I emptied FF at 1500 miles and used M1 5w20). Because I was getting this done, I brought my own oil. I stopped at WM prior and picked up Synblend 5w20 for this, the Sonata and EDGE 5w30 for the wife's Santa Fe Turbo. Well, when I showed the tech, he strongly recommended I use the 30 weight in the Sonata and advised me to go with a Xw40 in the turbo. I showed him where my manual makes no such recommendation for the turbo and he showed me their Tech Service book allowing for the Xw40 in the 2.0T (I didnt tell him I'd used it in the past). I asked why the recommendation and he said although dilution is normal, the less of it while staying within weight limitations, the better. They used the 30 weight and BOY, what a difference in engine sound. A lot smoother. Merk'.........you were right.