2006 Toyota Vios High engine temperature warning

Hi, I bought an OBD2 blue tooth scan, now I can monitor my gauge everytime I drive, the problem is, after I have drove the whole day until early 7 at night the high temp indicator flashes when temp reaches 96 degrees centrigate then fan starts to turn on, then authomatically turn off at 93 deg centigrade, I have replace a new engine coolant sensor and thermostat but the problem still goes on. But when the AC turns on the temperature become lower untill 88 deg. This car is a taxi. Can you tell me what the cause is?