2009 Hyundai Elantra sedan, 2.0l mpi engine, manual transmission. Currently 205,000 km on the odometer. Purchased new and car has been great. Starting in August my commute will go from 22 km (14 miles) round trip to 180 km (112 miles) round trip, all highway. Since the car has been out of warranty I have been changing the oil every 6 months regardless of mileage. The manual suggests for severe service 6 months/6000 km and I have usually been under that. Normal service is 12 months/12,000 km. I am going to try to talk my company into letting me work from home a couple of days a week. That will mean I am putting on at least 26,000 km a year and possibly 43,000 km a year. I have been using Pennzoil Platinum with an OEM filter. I may try Walmart brand synthetic at some point too. Would you run 6 months and 13,000 km (8,078 miles) drain interval? I don't think I would try 6 month / 21,500 km intervals, but probably would do 3 month / 10,750 km intervals if it came to that.