i have a 1980 Deville 368cid, im having a heating problem, i replace the thermostat, changed the heater control valve and flushed the heater core, i think the core is the same one from 1980 as was the thermostat, heater core flushed very well but still old, i even back flushed it please help...cold in the NW

 

what is the problem?
leakage?
no hot air?
no air at all?


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the air blows just fine, no leak just not hot,luke warm at best