I've started double checking the mileage calculated by the fuel computer and have found that it's consistently underestimating mileage by 1.0 to 2.5 mpg. Still pretty happy with the numbers, particularly the 6.5% commute and 10% highway improvement with synthetic oil. Keep in mind all of these numbers are using the 10% ethanol gas mix mandated here in Maryland, so mileage would probably be about 1 mpg more with normal gasoline. Highway driving - ~32.0 mpg (actually hit 34.0 mpg on one trip! ) Highway driving to the girlfiriend's place - ~29.0 mpg (75 miles each way, 95% highway) Some mileage stats for my 2007 GT Hatch 5sp Auto (using the trip computer):īefore Switching to Mobil1 5w20 synthetic:ĭaily commute - ~23.5 mpg (25 miles each way, 60% city / 40% highway)