My truck used to have super hot head and now it doesn't get as warm anymore. Would changing my thermostat make it Hot again?

well there are different temperature thermostat(temp equals pressure or steam that the coolant creates as your engine gets hot) which can let your engine run hotter or cooler. if you have never changed your thermostat before your engine wont run cooler, it will run the same or get hotter because it has become stuck and no longer allowing coolant to run as smoothly through your head which will actually make it hotter and eventually fail. as why your head is getting colder, who knows, maybe because its winter, driving distances, and how do you know its colder than normal? you use a temp finder?

Thermostats usually come in three heat ranges. 165,185 and 190 or 195 for most vehicles. A 185 degree thermostat will give you heat and is an easy inexpensive fix.

A thermostat works by staying closed, until the coolant reaches the pre set temperature of the thermostat. Then the thermostat opens and lets the coolant flow through the engine. When the coolant drops in temperature to about 10 degrees below the pre set temperature of the thermostat, the thermostat closes again until the coolant heats up again.

When a thermostat goes bad it usually either sticks open or closed. Stuck open causes no, or very slow heat. Stuck closed causes overheating.