Been having a problem with the heat in my 2008 Mustang for about a week now. The hear was taking a really long time to heat up. I checked and the coolant reservoir was empty so I filled it up. Drove the next day and everything seemed fine (heat got hot really quick). The next day, however, I was driving and notice steam coming out of the engine. When I opened the hood up antifreeze was coming out of the cap. I removed the thermostat and it was covered in rust and bad. I replaced the thermostat and cap just to be sure. I filled it back up and took it for a short drive. Coolant was still blowing out of the cap. Someone suggested I might have a blockage somewhere which is causing the pressure to go way up. I flushed the radiator out and the antifreeze was reddish brown. The reservoir was the same way. After the flushing I filled it back up again and took it for another test drive. I got like 2 miles when the car started to buck and then the wrench light turned on. I turned around and went back home. With all the rust I'm thinking either a severe blockage in the radiator or maybe a blown head gasket. I see no leaks anywhere (oil or coolant) expect for the antifreeze coming out of the cap and that only occurs wen driving. If the car is idling I have no coolant leaking from the cap. Also, during the test drives the temp gauge would go full hot for a few seconds, come back down to the middle and do this several times. Thoughts anyone?