Are you not operating LOP ?
Peak EGT, slightly LOP maybe.
My engine was taken apart in the USA and I have some good info and a good data point for an IO540-C4 which was frequently flown at FL200 and up to FL210:
The cylinders looked as I expected them to. The exhaust guides were worn
past service limits and the exhaust valve stems had .0015 thousandths
wear. This is completely normal on a high time engine in fact. Ring too
showed a normal wear pattern. To my eyes, you seem to have a very good
handle on how to treat a Lycoming engine.
I didn’t see anything that alarmed me to a oil consumption issue but
then again I didn’t dissect the rings with a microscope either. There
was no corrosion in the engine other than a slight amount on one of the
conrod beams. All in all a very clean engine core. While the cam will
need to be re-ground, it is not because of corrosion but standard
practice.
So… the high oil consumption – which was temporary, and was solved with some Mobil 1 0W20 in the last 5hrs of a service interval, repeated twice – left no permanent trace, and there was nothing wrong with the piston rings.
My conclusion, as previously posted, is that if doing these extended flights at the low power settings, one needs to intersperse them with some higher power low level flying. I normally do that naturally but on that occassion this didn’t happen.
I have an exchange engine now, just installed. Some details here
