So I was getting a combination 117 and 420 code. I just had the ca's replaced but it wasn't stock (my mistake). I decided to address the 117 code so I changed the Temp Coolant Sensor. After I did this I noticed the heat was increasing immensly so I tried to bleed the system. I had no luck but I was a first timer so I took it to a shop. They told me the head gasket was blown but there was no smoke, fluid looked good, etc. not sure if it just needed to be burped properly or what. I don't think the head gasket was blown and not sure how they came to that conculsion but i took it to another shop and they are looking at it now. I never ran it to the point where it was throwing on the "overheating" idiot light after i worked on it. It barely got to the "H" level. These garages were 1 mile from my house. I'm really hoping it's not a blown head gasket. Any thoughts would be appreciated.