The best mpg car I’ve ever owned was an early escort mk 3 turbo diesel, that thing must have done 80 mpg. It used to amaze me how little we filled it up.
It was bloody dangerous though as it didn’t move until the turbo spooled up, so right turns in traffic were exciting as you pulled out and nothing happened and then whoosh….it went like a rocket.
Blame emissions for some of the shocking mpg’s on some modern cars.