Why are you compleatly shutting the throttle in the descent? whould you not be better starting the descent a little sooner and not fully shutting the throttle, this would give you a slower ROD that is likely to be better for the ears of any passengers, and it would keep more heat in the cylinders to avoid any chance of shock cooling.
As for PFL's the best way to avoid shock cooling is to reduce the power by about 200 rpm just before fully shutting the throttle, this gives the cylinders chance to cool slightly and avoids shock cooling.
Some years back the British gliding association did some research into the shock cooling of cylinders and the recomended the slight reduction in RPM for a short time before descent, this resaech was conducted with a fully instrumented aircraft. The thrust of this research was to prolong the life of gilder tug cylinder heads but it makes very good reading for all who fly piston engined aircraft.
May be some one who is better with the internet search engine could find it!
Last edited by A and C; 22nd May 2010 at 11:30.