I have read with interest the speculation of aero engines verses automotive engines over many different threads and feel that the reliability issue needs to be cleared up.
In my previous life I was involved in the development and testing of engines for a major vehicle manufacturer for thirty years, managing the engine development area prior to my retirement in 2003.
The test regime on an engine is very severe with even a minor change to a piston ring for example requiring a number of 400hour wide open throttle (WOT) throttle test at maximum power(not 70%) to be conducted. These would run non stop except for regular oil change intervals. At the end of this test the engine would be torn down and inspected. Some engines would be rebuilt and run another 400 WOT test if required.
We would also conduct hot and cold cycle tests where the oil temp was elevated to 150+ deg C and coolant at 120+ deg C (under pressure) at WOT for 25 mins. The engine was then shut down all the coolant dumped. Cold coolant filled and started brought up to max temp at WOT for another 25 mins. This would be repeated for 500 cycles or more depending on what we were testing for.
The engine dynos were all computer controlled and calibrated regularly.
I have spoken to Rod Stiff a number of times on engine testing and he assures me that there is no aircraft engine manufacturer that conducts tests that are this severe or even come close, except for jet engines.
I have no doubt in my mind that automotive engine is far more efficient, reliable, economical and better built than most existing aircraft engines.
Cheers Helmut