What the hell were you doing at 18,000 feet? That is pushing it and ignoring the very real problems that can occur to both aircraft and humans. The standards you seem to be adopting are dangerous and haven't you heard of 'shock cooling?' Engines, especially Lycomings, do not like it and is not recommended.
Shock cooling a PT6A in a Cessna Caravan? Say again?
Flying at 18,000 is "pushing it?" How, exactly?
What was I doing at 18,000' dropping jumpers? Have you ever jumped or flown jumpers? How can you possibly ask that question?
What was I doing at 18,000? Flying a routine drop.
Very real problems that occur to both aircraft and humans? From flying at 18,000? It's done every day, all over the world, anywhere that aircraft are available to do it. Yes, 18,000', every day of the week.
This is a subject with which you're not familiar?
How do you "shock cool" a turbine engine again?