The 405's fan circuit has two speeds, so perhaps what has happenned is that
previouslyt, when your fan was always on, it was on the higher (and much more
noticeable) speed. And now that it is working properly (we assume), when it
gets to 190, it probably turns on the lower speed, which is less noticeable (ie,
not as loud). Perhaps a better way to tell if it goes on or not would be to
take off the front grille (two 10mm bolts on the engine compartment header, two
phillips screws on either inner side of the headlights) and watch the fans for
any 'action' as the engine warms up.
Adam Rodnitzky