What to do

replace the radiator? probably less then 200 if plugged, you might do a flow test with a spot thermometer to see if the radiator is plugged...take the temperature at the entrance and exit...then buy a new radiator~ also perhaps there is an electric fan with a thermal on switch that isn't comin' on~ you may check that...FLOW TEST...then NEW radiator~ that's my diagnosis~ 17 bucks from Amazon...cats love to chase the lazer too~ http://www.amazon.com/Etekcity-Lasergrip-774-Non-contact- Thermometer/dp/B00837ZGRY/ref=sr_1_2? ie=UTF8&qid=1455644847&sr=8- 2&keywords=spot+thermal+gun

if old now, have seen it with my own two eyes...the fins on the waterpump did not exist...only rust colored splines~ so yes, a flow test would tell ya~

dang PANIC, fill with water...get home and forget that you put WATER in there and a couple of days later RUST...and perhaps everything works okay for a time but things like thermostat stops and gets stuck open or closed....hope fersure you put a brand new 180 (yes lower) degree t-stat in there~ and did NOT use water...at any point in history!~

"the Whole coolant system" is what gets me....like then there is nothing left to replace...perhaps an electric fan is necessary to make sure it keeps it's cool...betcha didn't think about it's function as it relates to coolant temperature~ it's like...dude...show's over!~