What was found
LYCOMING SB 518C, DATED 5-2-95, STATES THAT THERMOSTATIC BYPASS VALVES (TBV), P/N 53E19600 WITH S/N/S 53788 AND HIGHER ARE NOT SUBJECT TO THE SB INSPECTION. DURING ENGINE REMOVAL, THE TBV (P/N 53E19600, S/N 56713) RETAINING NUT WAS FOUND SEPARATED FROM THE TBV AND LOCATED IN THE OIL COOLER. SUBMITTER RECOMMENDED TO REQUIRE HIGHER SERIAL NUMBERED TBV'S TO THE INSPECTION REQUIREMENT OF THE SERVICE BULLETIN.