Fan Changes Its behaviour

I Have Charade 86. Months Ago Its Fan Get Starts When Its Temperature Attant 30% On Gage And Turns Off As It Comes To 25-20% On Gage....... Now It Starts On 50% Temperature On Gage And Turns Of At Same Level 20-25% On Gage........ I Didn't Bring The Sensor out From The Engine I Just Clean Its Two Terminals.... (One Earth and Second Fan) But Still Acting The Same............
Should I Clean That Sensor by Bringing It Out From Engine?
Should I Replace It?
NOTE: As I Am From Subcontinent..... JUNE AND JULY are Too Hot Here...... Is It Possible That External Temp Effecting The Sensor.... Kindly Tell In Breif