Since the day I purchased the 2018 MKX, when filling the tank it has always been an annoyance why one time the range reads 280 next time 330 and so on. Now the most recent odd occurrence is when I use premium gas versus regular my range jumps up to 400+ miles. With premium, I do get slightly better milage from maybe 17.3 to 17.8 but should not increase the range by 100 miles. I have tried different stations figuring maybe the nozzle shut off is different but never was able to get a range of close to 400 with regular!