So I have an 01deville and it has almost 100k on it. I bought it 2 months ago used and it started overheating after a week. Had the system purged manually and it worked fine.... for about three weeks. Then overheated again. Looked at coolant, it was about half a gallon low so I added some. Ran fine. Then I replaced the surge tank and it was good. Then today I parked it on a hill for not even 5 min. When I came out the DIC was going crazy. "Engine coolant hot- idle engine" "engine hot - ac off" "change engine oil" (which is weird considering I just changed the oil 3 weeks ago). There was No ac Running and I let the engine idle after backing the car down off the hill. "Engine overheated - stop engine" so I shut it off, let it cool down turned it back on. Drove a mile and a half and it overheated AGAIN. Had it towed home and here I am. Someone, anyone, ideas?