If the temp gauge doesn't come up around halfway and stay there, you've got a problem somewhere. My car would seem fine in summer here in GA, but when it got cold it would seem to warm up just as I finally got to work (15 mile drive, all at 65-70 except the last 2 miles). Then I figured out that if I drove for a little bit then stopped it would come up to temp pretty quick. As soon as I took off and hit around 40 the gauge would drop like a rock (and you could feel the dash vents go cold). Replaced the thermostat, little to no differance. Started to doubt myself. Came to my senses, bought a name brand thermostat and been nice and toasty ever since. You don't even want to know how many house brand parts from one of the big chains are bad out of the box.

You could cover up part of the radiator with cardboard as a quick fix, but that's just covering up the problem.