What was found
(CAN) AFTER OVERHAUL THE ENGINE WAS RETURNED TO SERVICE. AFTER A 35 MINI TEST INTO TEST FLIGHT THE CYLINDER HEAD TEMPERATURE OVERHEATED, 340F. THE ENGINE WAS SHUT DOWN & THE AIRCRAFT, TWIN ENGINE, RETURNED TO BASE. INITIAL TROUBLESHOOTING REVEALED THE WATER PUMP IMPELLER WAS DETACHED FROM THE IMPELLER SHAFT, THE IMPELLER THREADS WERE COMPLETELY STRIPPED & THE WATER PUMP HOUSING & IMPELLER BLADES HAD SIGNS OF CONTACT. THE ENGINE WAS RETURNED TO THE OVERHAUL SHOP & FURTHER INSPECTION REVEALED FOREIGN OBJECT DAMAGE TO THE IMPELLER & PUMP HOUSING. THE COOLANT SYSTEM WAS COMPLETELY FLUSHED, INSPECTED BUT NO FOD WAS FOUND. THE ENGINE WAS INSPECTED TEST RUN & RETURNED TO THE OWNER. THE INSTALLER WILL REPLACE ALL COOLANT HOSES & RADIATOR TO AVOID RE INTRODUCING ANY FOD INTO THE ENGINE.