I recently purchased an Alero. The car keeps overheating. I have replaced the radiator, coolant resevoir tank and has a new thermastat. I am constantly pouiring antifreeze in the coolant tank. There are no leaks. The car goes nearly two blocks then overheats. I wait five minutes then release the pressure from the coolant tank then go another two blocks. I was told to bleet(?) it but that part(?) is missing. Any idea what I need to replace at this point? Any insights are helpful. Thank you.