Okay, if I am reading this correctly you replaced the pump, thermostat hoses and such. Filled it with coolant and now the engine heats up and your heater works on/off. Yep sounds like either air in the system or the new thermostat is bad (has been known to happen)
The system is self purging but the hose to the surge tank could be plugged or the cap could be bad.
From the book.
1. Refill the cooling system. In order to ensure sufficient engine cooling, freezing and corrosion protection, maintain the protection level at -37 C (-34 F) or lower.
2. Start the engine.
3. Place the heater and A/C control in any A/C mode except Max and the temperature in the highest setting.
4. Allow the engine to continue idling until the lower radiator to water pump hose is hot.
5. Turn off the engine.
6. Allow the engine to cool to outside temperature. Ensure the coolant level in the surge tank is at the proper level.
If this does not help then I would pull the purge line off (3/8" line that runs from the water pump to the surge tank) and check for flow while holding it over a bucket. At idle it should at least spit some coolant out, rev the engine and it should flow a steady stream. If nothing pull the other end off and blow air through the line. If it is clear and you do not get flow, add some more coolant.
If still nothing, it is time to pressure test the system to see if it holds pressure. Sadly the N-Star has a bad history when it comes to head gaskets.
Tuesday, December 13th, 2016 AT 3:59 PM