Ron brings up a good point - the thermo-switch might be on the cooler output and never getting hot enough to kick in. Also, I don't know (and neither do you) what temp your engine is at when the silly, number-less, uncalibrated temp gauge is at mid-scale. The only way you can tell is to use a dip-stick thermometer and then mentally know that, "OK, Mid-scale is about this" and go from there. Personally, I drew a green line on the glass face of the gauge showing me where "normal" is which, for my car is about 200F, just in case my son is out tearing around in it.
As an aside, I took Pearl out the other day (about 34F outside) to get inspected in the Cod-Fish state, and the temp gauge got about a needle's width up off of the lower end of the scale....two needle's worth by the time I got home. Brrrrrrrr...... It's a good thing I don't have heater boxes or I would have been complaining about the lack of heat in the cockpit!