I bought a 2008 impreza wrx hatch about a month ago and just recently started having over heating problems. I’m not not mechanically challenged but this one baffles me. When ever I am driving the car it will randomly (within about 10 mins usually) it will start over heating. At first it seemed like a faulty thermostat or that the system was not bled correctly so I replaced the thermostat and bled/burped the system correctly and sure enough it still overheated the fans kick on so I crossed that out but then the car started blowing off coolant all over the engine bay from right around the Reservoir I then noticed that there was white smoke coming from the reservoir when this happened and it would also come out of the radiator I felt both of the lines and the top one was very hot but the bottom one was cold so that led me to believe there was air in the system still because I had just replaced the thermostat. I decided to run a test and run the car without a thermostat and sure enough there was no heating issues even after running for a long time it stayed right at running temp nothing less nothing more. So that scratched off the radiator being faulty because if it was the car would over heat with or without the thermostat. I have also notice that the reservoir with the thermostat in overflows like all the way to the top. My thought is that I have a minor head gasket leak, I believe that it is releasing a very small amount of exhaust gasses which will gather around the thermostat stopping it from opening like if air was in the system. I’m not having white smoke coming out of the exhaust or milky oil so I think it is very minor but still causing over heating with the thermostat in could anyone give me their input and tell me if I’m diagnosing this wrong or if they have heard of this same problem?