The window sticker fuel efficiency rating was established using controlled driving, that is: no traffic jams, vehicle at curb weight(no passengers and cargo) and driven on long distances. The average mpg is then averaged. Don't expect your car on your road conditions and distances you drive to do the same. You'll just get frustrated
I had the same experience with our Ford Fiesta Ecoboost. I'm only getting 6km/L and that's mixed city and hiway driving. Now after the 1Tkm mark I'm getting 9-10km/L mixed also. Basta hindi ko ilalagpas ng 3k rpm kase doon gagana ang turbo ng ecoboost yun daw malakas gas saka 60-80kph lang speed ko. Hehe! Try mo Total Excellium or Seaoil 95/97 or PTT okay din kase meron samin. Okay naman performance nila.