S60 2.4T Fan Problem – HOT

Hello – my S60 2.4T 8/2001 has a problem: During the ride it keeps perfectly 90°C cooling average emlerature. I noticed by chance in the Torque that it goes clearly up at the stand (have stopped at 104°C). After that I caught my little Volvo tester. Both fan levels are off without air conditioning. I activate the climate, goes fan level 1 to ON. Temp rises however as said over 90… When should fan 2 trigger and what activates it? Recently I kicked it half way, then the fans ran after full pot – so as the fans still went without problems. Thernostat is also new since I have never reached more than 78°C in winter… Thanks for your help!!!