Nissan Repair Questions? Ask a Mechanic for Answers ASAP
You have a air lock in the cooling system , what I do is jack up the front of the car with the radiator cap off with a coolant funnel on top of radiator with coolant in it raise the cap above the engine, so the air will go to the highest point to get air out , let it idle with heater on until it start to blow warm then the air is all out, then put the cap back on , if it does it again you could have a head gasket starting to go letting air into the system, Thanks let me know if you have more questions, ROY!
You still have air in system you will need to get it bled out so the heater will work correctly. Thanks ROY!
It will not get as hot as when rpm is up, but if warm at idle you are ok, Thanks ROY!