Currently have been using Mobil 1 Extended Performance 5w30 in my 2.0L Kia Seltos (non - turbo MPFI engine) and 2.4L Sonata (non - turbo GDI engine) . When I buy the above oil at Walmart , I always see the Mobil 1 Full Synthetic 0W40 for about the same price and have been somewhat curious to try ? My OCI’s are average (5K miles max / 6 months) of mixed city / high way driving in temporate PNW temps. *I have no complaints with the current Mobil 1 Extended Performance 5W30 but wonder if the Mobil 1 Full Synthetic 0W40 beats it out for all the important specs that improve the life of an engine (wear , cleaning , performance , protection , etc. ) over the Mobil 1 Extended Performance 5W30 oil? Lastly, my vehicles don’t list a 0W40 being approved in the owners manual - while doubtful my engines will blow up running 0W40 , I have refrained from using any oil grades not listed in the OM (5W20 , 5W30). Your experiences making the switch from 5W30 to the newer Mobil 1 0W40 oil with its even higher 13.2 cSt rating (probably higher HTHS as well)?