The stabilizing effects of centrifugal forces, for slightly heated airflow in a 180 degrees curved square channel with nearly fully developed entry flow, are studied by temperature fluctuation measurements for Reynolds numbers in the transition range, Re = 2000-4,500. The relaminarization process is caused by secondary flow due to centrifugal forces. This study confirms Be feasibility of using a fine thermocouple (12.7 mu m) to study flow transition phenomena. The results are presented in both time and frequency domains.