Ford Fiesta cooling fans

My engine cooling fans have started to come on for no apparent reason. while i am driving my temperature gauge as normal shows the temperature balanced between hot & cold, and then all of a sudden my fans will come on, and remain on until i have switched off my engine. i had my wheels and brakes changed saturday just gone and my temperature gauge shot up to the hot zone and was slowly going back to being cold then between hot and cold. i topped up my water with anti freeze on sunday and still the fans come on, my oil looks fine although i wil check again in the morning. i think i noticed a leak underneath my car on the saturday but took no notice of it.

any ideas, thanks. its going in for a check wednesday