Called Hyundai- they said it was Quaker State. Seems they are pushing this brand. Manual "recommends" it. I have no problem with this brand, but seems ridiculous that one particular brand would work better.
We have two Hyundai vehicles and noticed the same thing. We ran the factory fill for about 3500 miles then switched to synthetic 5W20 oil.
We live about 100 miles south of the Montgomery plant just north of the Florida state line and run 5W20 oil year around.
The 3.3 liter V-6 is made here in Alabama in Montgomery and they are expanding the engine plant and soon will make the new 4 cylinder engines too + they will be making engines for the new 1+ Billion Dollar KIA Plant being constructed in West Point Georgia about 40 or so miles east of the Montgomery Hyundai Plant.
The Santa Fe and Sonata are made at the Montgomery Plant.