Only about 18,000 so far. No problems. We had a 2008 before that (had the 5.4 V8) and put 120,000 on that one with few problems.
The Ecoboost has been good in the Expy, and also two F150 company vehicles (2015 and 2017) in our fleet.
If you're looking at a used Expedition, maybe a 2016 or 2017 model would be a good buy. Some people don't like the looks as much, but I'll tell you I much prefer the lower price and actually I think the visibility is better. Also, it's easier for my short wife to access items through the rear hatch (window glass) of the old expy. But the new interiors are pretty great.
