Food for thought, take your thermostat out, put housing back on, disconnect top radiator hose from radiator, disconnect bottom hose from radiator, put as much water thru the block going from top hose so it all comes out the bottom hose (obviously), once it seems to run clear, try pushing water up the opposite way from bottom hose to push water out of the top hose.
By doing this you flow water in the normal direction, then by reversing the water flow you remove scale and build up that has clung on with the normal dircection of flow.
repeat process for the radiator also, dont forget to put your thermostat back in either
There is a tool that you connect the water hose to and also an air line to force the water thru in both directions, not sure of the tools exact name but it "power flushes" the system.
Hope that has helped.
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