As said before, piston and sleeve temps are much more than the outer cylinder especialy the exaust side of the piston. When the engine shuts down the heat transfers very quickly from the piston to the sleeve and then to the crankcase and cylinder head. It is true that the engine needs heat to break in but running nitro with the fuel, generating heat is the basic by-product and without water or large cooling fin head temps can soar and piston melt down will happen.