How many thousand kilometers need to overhaul the engine.
Overhauling engines isn't part of regular maintenance. A top competition drag racing engine might get overhauled every mile or so. Granny's car that's driven and maintained well might never need an overhaul. I have a 1991 Toyota Previa and have noticed that most of these I've seen for sale have three-hundred-thousand miles on them and those engines have never been torn apart. Drive your Mirai well and you might not have a problem until the next millennium.