If you aren't familiar with the temperatures that are present in a properly functioning engine, then it is best to do some prepartory work. That way, when you do have a problem, you can diagnose it without any fancy equipment.
Start the engine cold and let it warm up. Place you hands on the various components, EXCEPT THE FAN
, as it is warming up. That is the radiator, hoses (radiator and heater), block, area where the sensor is, etc. Make sure to cover the area of the thermostat as it opens. Also, have the radiator cap off and watch the fluid. Before & after the tstat opens, have somone accelerate quickly if there is someone available. Watch the fluid in the radiator to see what it does both before and after tstat opens.
Now you have a base of information for what it should be. When you have a heating problem, you can check it out without fancy equipment, which you likely won't have available, even if you do have them back in your garage.