I have a Mercury Villager 1996

I have a Mercury Villager 1996. In winters when the outside temperature is below 5 deg C, the enigine temperature shown on the gauge does not go above cold (C) even after idling the car for almost 20 minutes and driving as long as 20 minutes.
It works normal in summers.
If the heating system is turned on, it makes noise as long as the enigine temperature comes up to normal.
Please suggest the root cause and possible correction.