@Flakbadger & Daox
Thanks for welcoming me and I appreciate your instant help!
I have noted my fueling data for a long time on a german website called spritmonitor.de. The total average from 0 tot 100.000 km (60k miles) was exact 54 MPG. But after a few years without keeping it up with it, I notice that the engine runs smoother and better with age. So it's time to pick up some new data and optimize the car.
I saw some awesome things on this beautiful forum like grill blocks and moon discs, those are quick wins = not expensive and easy to install.