OP here : I just hit the 6-month mark with 2,635 miles on the oil (Valvoline Advanced 5W30) with a ST 10K mile #9688 oil filter . 2017 Hyundai Sonata 2.4L GDI (non-turbo) . Oil was black with soot and smelled of fuel in a well-kept engine since new with 4K mile / 6 month OCI's . PCV valve was changed 3K miles ago at 41K miles (Original PCV valve was still in good shape - but low cost and easy to change on this engine so I figured why not ?) Most trips were 15 miles or less to work , gym and running errands , all in the suburbs with an occasional (monthly) interstate run at high speeds for 30+ minutes. I could never see an OCI longer than 6 months with my current driving routine with this vehicle (no matter the oil) and next OCI time will be dropped back to 4 ~ 5 months while monitoring the oil. Perhaps if I had a daily commute of 50 miles non - stop on an interstate at higher speeds my oil may have been in better shape at the 6-month mark , it's hard to say ? On my new oil & filter change today I used Valvoline 5W30 EP and went back to my preferred Fram Ultra #9688 oil filter. The ST #9688 oil filter I just changed out with its hard , beveled rubber gasket had leaked oil around the edges of the oil filter even though it was tight and the metal engine mating surface was spotless and always cleaned any way prior to installing a new oil filter. Lastly , make up oil over the last OCI was about 3/4th of a quart . Best case , this write up will help others with a similar Theta II 2.4L GDI engine - worse case BITOG followers can see what type of OCI's other folks are achieving here with different vehicle makes and engines .