I’m not interested in the TBO or problems which develop slowly and which can be caught in time. My question was after how many hours, in average, you think a catastrophic failure can be expected with a Lycoming or Continental aircraft engine? I believe I heard numbers of around 20,000 hours. This would be about 10 times the hours of what I experienced with series production Diesel vehicles and what seemed pretty much the standard, compared to colleagues and friends. All the catastrophic failures were caused by some kind of electronic problems, the only mechanical problems I remember were failed turbochargers and a failed high pressure pump, these were however rather slowly developing issues. I am talking about a.) humming along, fat, dumb and happy and the engine going dead from one second to the next and b.) on top of that, humming along, fat, dumb and happy and the engine going to fail-safe mode, reducing the available power to maybe 10 - 15% If a.) would happen every 2000 hours and b.) every 800 or so hours in an airplane, I would guess that most pilots would quit flying. ECUs, sensors, electric injectors all tend to crap out without any warning but are essential for the operation of a modern Diesel. Just think about the enormous investments which already went into the development of the aircraft diesel engines. Well funded companies went bankrupt over this, even though they also used proven car engines as a basis. To turn a car Diesel engine into a reliable aircraft engine, which can also be operated with Jet fuel, is not even remotely as simple as it looks. Personally, I might fly behind a converted car gasoline engine, if it is well executed, because of its lower complexity and because components which are prone to failure and critical for the operation of the engine can more easily be made redundant. A converted Diesel – no, thank you, unless serious efforts went into the improvement of its reliability and the redundancy of critical components.