from the way you explain,it sounds as if coolant isnt flowing...you may have an air pocket in the system.
lets try this
lets bleed the system this way
1-remove the radiator/reservoir cap when the engine is cold
2-start the engine and let idle
3-turn the heater on max
4-keep coolant on hand and add it as needed
5-spme coolant may gush out with the air
6-keep doing this until the engine is at operating tempeture and the heater is hot
7-after the coolant settles down and the engine is warm,,install the cap
This may take as long as 20-30 minutes
let me know if that fixes your problem
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