Wont warm up even with new thermostat

[acat550]

Hey guys,
I have a 2001 Alero 2.4l and live in Saskatchewan where it gets cold, up to -40C in winter. My alero however doesnt like to warm up. Last winter I changed the thermo with a stock one, 180 deg. and still the same problem...the temp gauge barely gets past 1/4 and heat coming out of vents is a huge issue for defrosting! I put a carpet infront of the rad, but that still didnt completely solve it, yet helped somewhat.. Im in search of major help as I have no idea what else that could be causing this problem? My gf has 3.1L alero and hers warms up great, but dont no anyone with a 2.4. Would could possibly be the problem because its killing me with the lack of heat with the car not warming up. Ps-It dont even warm up regardless how long I drive it.
Thanks