What was found
AS AIRCRAFT ROTATED DURING TAKEOFF, MANIFOLD PRESSURE DROPPED, PILOT FOUND LOW OIL RPESSURE, AND RETURNED TO AIRPORT AND SECURED ENGINE AFTER LANDING. ON INSPECTION, FOUND OIL COOLER BOWED OUTWARD AND INNER COILS BULGED WITH 2.5 INCH SPLIT. OIL COOLER WAS OVERHAULED APPROXIMATELY 120 HRS. NO APPARENT DAMAGE OTHER THAN LISTED FOUND ON COOLER. FOUND NO REASON FOR COOLER RUPTURE. ON ENGINE GROUND TEST, ALL ENGINE PRESSURES NORMAL. (X)