Hello to everyone, I'm starting to wonder if i did the right thing during all this time, changing my oil every 7000 to 8000 kms (4 to 5k miles) using cheaper 5W40 synthetic with 229.3 spec. I mostly do highway driving and country roads (500 kms a week) with a few short trips but little city driving. The car is a 1998 Mercedes C180 in perfect condition with 150k kms and i plan to keep for a long time and the highest mileage i can. It only runs E85. Is E85 a good reason to keep my OCI short ? Should i continue with shorter OCI and 229.3 oil ? Change the oil every 15 000 kms as recommended in my car's manual, maybe with the highest spec 229.5 and change the filter once between oil changes ? I dont want to compromise the lifetime and performances of my engine but i feel like i am wasting money and good oil sometimes.