This is one of the most helpful cooling system 3d vids I have found, that gives a complete rundown of how the whole system works together.
Please note how the thermostat modulates to keep the temp at the "stamped" temp, and only opens fully when the rad cannot cope with the heat being created.
Low heater temp in winter is usually a stuck full open thermostat, - the rad capable of shedding +/- 60* of heat lowers the coolant temp way below comfortable, - the heater blows cold air, cuz the thermostat isn't partially closing to modulate the coolant.
Watch the vid, particularly the operation of the thermostat, skip the ad.
Cheers