Champ wrote:
... automotive engines
for aircraft ... have a very hard life.
Take-off and climb is full power or very nearly, then they throttle back to
cruise at 75% or thereabouts. The only roadgoing vehicles that approach
that sort of use are in motorsports, and how long do they last?
....
It's perfectly possible to tune and engine to the load you describe
*and* achieve high reliability.

SW Oklahoma is arid, so there is plenty of business for engine
rebuilders, dealing with the farmers who run (ex-) auto engines
at high load - day and night - for the irrigation season. The hours rack
up fast.

I talked to one builder 2 or 3 years ago. Details escape me now, but the
approach was not that dramatic, to produce a 10 thousand hour engine BMO
That's when an engine doing 2000 hours in a season, lasts several years.
They use auto cutouts for low oil, and hot cooling water of course.
Oh yes, they tend to run them on natural gas. That's quite a favorable
factor, apparently.

The load is relatively kind, it's true - a water pump: kinda like the
fluid flywheel on an automatic. The bores are hard chrome, the valves
are metal cooled, the seats are hard-faced inserts(If I remember...)
some other details of that kind.
The oil changes are a religious ceremony.

Brian W