A thermatic fan is designed to run only when it’s needed. As the name suggests, it should switch on when the engine attains a pre-set temperature and then turn off below that temperature. It’s a way of having the engine run at a more constant temperature as well as saving the power normally used to run a fan that isn’t needed the whole time. Sometimes, a second electric fan will cut in when you turn the air-conditioning on, but the short answer is no, a thematic fan should not run all the time.
