Well, it's hard for it to be the thermostat, as it's been removed. We took out the housing and it was simply gone. As best I can tell the old owner removed it for some reason. One guy told me that it's fine to take it out here because it's always over 80°F outside. I will be putting one in as I get this fixed.
Oh, and.. from my original post: "Also, the last time I saw the guy drive around the block with the car I saw white smoke coming out the back. Which leads me to believe that I now have a blown head gasket."