I have a 99 poniac grandam se and it had two blown heads when I bought it. I had the heads shaved so they where like brand new. My car has been good for about three years an it just started acting up again. It is overheating very bad to the point I can not drive it one block. And the heat works when it wants to. My husband replaced the radiator and it didn't fix anything. He also replaced the thermometer. Could it be the heads again or is there another problem?