What was found
DURING A 100 HR INSP, IT WAS DISCOVERED THE THERMOSTATIC OIL COOLER DOOR WAS CRACKED ON BOTH ENDS AND A SHEARD RIVET ON THE RT END. THE COOLER DOOR IS CONTROLLED BY A THERMOSTATIC VALVE INSTALLED IN THE OIL COOLER AND OPENS AND CLOSES TO MAINTAIN PROPER OIL TEMPERATURE. THIS IS THE SECOND OCCURANCE FOR THIS ACFT . THE FIRST FAILURE WAS FOUND AT 1566 HRS AT WHICH TIME A NEW DOOR WAS INSTALLED AND RIGGED IAW INSTRUCTIONS. PRESENT ACFT TT 1981.6 HRS. THE CAUSE OF THE FAILURES ARE UNKNOWN AT THIS TIME BUT SUSPECT TOO LIGHT OF MATERIALS AT MFG. A CAREFUL INSTALLATION WAS CARRIED OUT ENSURRING NO EXTERNAL LOADS ON THE DOOR WERE PRESENT.