Need help to trouble shoot the overheating problem I have. The issue is that my 2000 Celica GT overheats when I drive it, does not when it sits at idle. I just purchased this car yesterday. I have noticed yesterday that my car overheats when I was driving it back home. I pulled over a few times to let the car cool down before I made it home. I noticed while I was waiting for the car to cool down that the cars lower coolant line was really hard, upper was not. Lower was warm but upper was really hot. So today I went to replace thermostat and to my surprise there was none. Funny thing is that the seal was but no thermostat. So that really assures me know that the issue was not a stuck thermostat. Water pump seems to be fine also. What could be the issue gentlemen? Do I have a blockage in the head or somewhere, to where the coolant is not passing through the way it should?