[V6-12v] coolant cap.

[Clive Young]

Okay so i  am still fighting the no heat condition ! But I do have a whole bunch of new theories and I have lots of test data. I will present my findings later but for now I have a general question and am wondering if someone can do a simple test for me. 

One of the things I am doing  ( maybe incorrectly ) . is pressurizing the coolant reservoir when the engine is cold, then I open the bleed screw in the top of the heater hose and air always comes out. I leave it until there is coolant coming out and then I close it . This happens every time ! What I don't know is am I putting this air into the system by pressurizing the coolant overflow. am I pushing air through the small overflow tube , into the rad and through the top of the engine ?  ireally don't know if this a proper test. I tried pinching that line off and nothing went anywhere, so obviously the lower coolant line must go to the closed thermostat. 
    My working theory is that I have air in the heater core that I can not get rid of , or I am inducing it ! 
    As the engine cools down I thought it drew coolant into the engine, on my car every time I take the reservoir cap off  when the engine is cold i hear a small amout of air being sucked into the tank. Is this normal , should the tank not be vented ? . I f someone could do this same test for me I would certainly appreciate it. My theory is that if this cap should be vented and it is not , my engine as it cools is pulling air past the bleed screw into the heater core every time under vacuum. I know it is a long shot , but hey , I have tried everything else ... I have tried the bleed screw open during starting until fluid comes out but again the next day when it is cold, my "test " shows more air in the system. strange ....
just to recap ...
Engine runs and cools normally , fully warmed up the temp guage sits just under 90 and the fans come on just over 90 after idling for a while. On high idle I get lots of hot air, idling it cools off rapidly ( within a minute ) . I have changed, water pump, thermostat, cleared and flushed and checked heater core. The car never overheats in the hotest days in the summer ( cooling system okay ). I have checked the blend door ( manual controls ) , checked the blower input for debris. Still no success. 

    As a side note a good little afternoon project for those of us that anal is to pop off the wiper arms , turn the lockdowns and take off the black "cowling" cover off the area at the back of the hood and under the wiper arms. You can then completely clean up the air inlet to the blower fan and grill , and inspect an clean and lubricate the wiper mechanism ( mine had a bolt ready to fall right off ! ) . I also washed and waxed the shiney red pint under there .... My car was actually that colour once ???? 

Have a great day guys ..