So will the iron out I suggested.it was originally marketed for cleaning the same type of deposits out of boiler radiators, and I have some old Prestone flush cans that are exactly the same thing (sp?) Oxalic acid. Flush with water til as clean as it can be, add a cup of iron out, finish the fill with water, drive a bit to circulate it, if real bad let sit with this in it over nite, pull block drain and radiator drain and flush with water again til clean, fill er up and let er rip
