I run w/ water & 1 lb citric acid (ebay) for a day, flush many times w/ block drain plug out. I install a screen in upper radiator hose to catch stuff and not clog new radiator. I thoroughly dry (esp. heater core), change to silicone hoses and run Evans Waterless Coolant. Then no more corrosion or worries. Note the new water pump needs a gasket on each side of the metal plate.