What was found
RETURNED TO DEPARTURE, DUE TO SMOKE & FUMES IN THE CABIN AND COCKPIT. VISIBLE WHITE GRAY HAZE. NO EICAS MESSAGES. BEGAN ON CLIMB OUT, ACCOMPLISHED FIM TASK 21-20-00 FOR SMOKE ABNORMAL ODOR. NO SOLID FINDINGS FOUND DURING ANY INSPECTIONS. NOTICED THE LEFT RECIRCULATION FAN CYCLING ON AND OFF SEVERAL TIMES. R & R THE LT RECIRCULATION FAN AND FILTERS. SUSPECT POSSIBLE PRESERVATION FLUID RESIDUE DUE TO FIRST FLIGHT AFTER NR 1 ENGINE REPLACEMENT . PERFORMED 25 MIN ENGINE RUNUP WITH 2 HIGH POWER RUNS. ALL CHECKED OK.