@ COCyclist: thanks for that info!
Winter is still a long way off, we are currently experiencing a 'super heat wave' (as it's told in the media), with temperatures of 90 to 100°F for a period of 9-10 days. That's quite unusual for my region.
So I removed the grill cover again. My driving style during this tank is more normal (read: faster) but because I have refined my driving techniques I'm getting a consumption of 63 MPG. I only put the airco on occasionally with my wife and children in the car. Their well-being is more important to me than my quest for good consumption figures ...
So no, this tank will not be a new record.