Hi Merc1,

I don't know your car, but I assume the coolant flow is from reservoir back to radiator, then to thermostat housing, then engine and then back to reservoir, once operating temp. is reached, i.e. thermostat is open. So if you reached operating temp, the antifreeze has completely mixed. On my 87 420, I can feel the rubberhose between radiator and reservoir getting hot, which means coolant is flowing.

You flushed probably the reservoir, radiator and hoses, but not the engine.

Regards

Reinhard Kreutzer