What was found
HEAVY SMOKE (BURNED OIL) FROM NASI'S NUMBER 1 AND NUMBER 2. RETURN TO MIAMI. FOUND OIL RESIDUE AT INPUT PORT NR 4 HEAT EXCHANGER. REMOVED AND REPLACED NR 4 HEAT EXCHANGER IAW DMM 36-1-3, SYSTEM OPS AND LEAKS CHECKS GOOD. PERFORMED GROUND CABIN PRESSURE CHECK IAW 21-6-0, NO DEFECTS NOTED, NO SMOKE IN COCKPIT. CHECKED PNEUMATIC BLEED SYSTEM FOR ENGINE 1 THRU 4 INDEPENDENTLY, NO DEFECTS, SYSTEM CHECKS GOOD IAW DMM 36-1-2. VERIFIED PROPER ENGINE OIL SERVICING IAW DMM 12-1-0. PERFORMED GROUND IDLE / TAKEOFF POWER RUN IAW 71-00, ALL SYSTEM CHECK OK.