I have a 99 lumina with a 3.1. While getting my window fixed today, it cut off. I started it back up and noticed the temp hand was all the way up. I turned it back off. I felt the radiator hoses and noticed they were cold. The antifreeze was cold also. I replaced the thermostat thinking the fluid wasn't flowing. That didn't help. I noticed large air bubbles in the reserve tank when I started it back up after it cooled down. What does that sound like?