well the cooling fans don't run all the time. there's a switch in the radiator that closes when the coolant hits a certain temperature. at least one fan should also run whenever the A/C is on. flushing and filling really won't change that, neither will doing the thermostat. as long as your temp gauge doesn't skyrocket, I'd just shrug it off.
Mine was like that since i bought it but come summertime i got worried about overheating and didn't feel like changing several things till i figured it out, so i just wired a switch with some heavy guage wire and turn it on in the summer when i'm stuck in traffic etc. So far so good!
Mine did not turn on because I had 1/4 of the coolant left... not enough to activate the sensor fan. Every time I replaced coolant, it would leak... out of the waterpump weep hole. So now I have a new pump! No more leaks!