I have been having overheating issues with my 2005 Civic EX (5 spd) for the past month or so. After being in traffic for a little bit, my temperature gauge maxes out, and my vents blow cold air. Not even luke warm air, it's cold until I start moving at a constant speed over ~45. So I recently flushed the radiator fluids and refit all the hoses with no prevail. I took it to my local mechanic and had my thermostat replaced, and the problem still persists. So I had it back at the shop today, and they checked my compression in my cylinders. As I understand, normal compression is around 130? Three out of four cylinders passed, and the fourth read at 100 (I hope that makes sense, as I am not a savvy car guy.). My mechanic suggested this might be related to a bad head gasket, and it would be 4-5 days worth of work. I just wanted to get a little more insight online before I take it for a second opinion. Does this sound like a head gasket issue, or what else would cause the car to be overheating? Please let me know if you need anymore information related to my car, I'll be happy to provide as much as I can. Thanks in advance.