Got to love the mountains
 

I got my best trip mileage ever and one of the best tanks ever as well driving though the tallest mountain passes I've ever travelled with this car. Averaged 6.85 l/100 (34.3mpg) for the trip and averaged 6.67 l/100 (35.2mpg) for 930 km. Scangauge showed a trip average of 5.6 l/100 for a 140km stretch which included a 400 meter climb but it was downhill overall. Still, that's 50.4mpg from a car that is only rated for 26mpg highway. It's an auto so can't do a lot, but slow speed limits and DWL did it I think.

Rolling hills gives me the best fuel economy out of the Focus.

I had a similar experience years ago going cross country to Seattle in my manual shift 06 Mazda 5.

The car hovered at around 30 mpg for the trip and when I headed into the Cascade mountains I figured that my mileage was about to take a big hit. As it turned out, mileage was a tiny bit improved on that stretch instead. I have to assume that all the extra fuel burned climbing was compensated for by all the engine braking on the downside where the injectors were completely off.

I remember thinking at the time I would not want to have had an automatic on the downside. The manual shifts engine braking was at times not enough to check decent speeds, the engine at zero throttle and rpms hovering at 5 grand and above for miles. I can only imagine the brake wear that would have occurred in that situation by having to rely mainly on the brakes instead.

Dean