1999 Monte Carlo 3.1. Just replaced the upper & lower intake manifold gaskets and new thermostat. Now the heater is not blowing hot air. Part of the problem was an air lock. Refilled the radiator & reservoir. Better, but not as good as I think it should be. Is this a hot water flow control valve that is mounted on top of the water pump housing. One rubber hose comes "in" and the outlet is a steel tube that goes around the engine into the heater core. There is an adjusting screw?? on the top side. Can I open this a little to improve the flow through the heater core?

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yes that is your bled valve

 

that is your bleed valve.put a small rag around the housing.then open the screw up untill you see coolant/antifreeze come out.if you do not see ann coolant squeese the radiator hose to ge the air out.good luck dominic