I have no idea how guys are getting upper 30's to low 40's for MPG in a GTI. I average 20-23 City on Summer blend, same driving on Winter blend is 18-21 City. If I really baby it I can coax another 2-3 mpg. But I can't baby it for long, why would one want to
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If I put it in Sport and manually shift my DSG I can see the fuel needle move as I drive more aggressively and then I'm seeing 17-19 mpg or less.
Highway, cruise set at 75 I can get 31-33 with no wind and no asshats hanging out in the left lane or having to pass idiots that don't know how to use cruise control. Most time I average 29-31 for a 150 mile trip.
I honestly don't believe people that say they get 39-43 MPG. That's way outside the EPA and manufacturers ratings. Somethings amiss in your math or you're not telling the whole story. The GTI has always been a jekyl and hyde when it comes to mileage. If you drive it very conservatively it will give decent mileage, but the minute you start driving spiritedly, the mileage suffers. I fall into the latter. I don't beat on the car, but I don't drive it conservatively, not sure I could drive it conservatively...……...it begs to be driven with a certain amount of zing and playfulness, so I oblige.
Just my .02c