If your not getting heat inside the car, it's most likely not air or a failing temp sensor. My girlfriend had a Subaru 2.5GT that actually had a leaking water pump. It ran fine but was slowly loosing coolant until it finally reached a point where it was too low to function and the car overheated. I ended up putting a bottle and a half of that pre-mix antifreeze in it just to top off the radiator and get it home. If you've got a small coolant leak you could have a similiar situation. Have you tried topping off the system to see if there is any fluid missing? Can you please deliver me some large plain cheese pizza's too (there's no Papa John's within delivery range of my place and I miss it so much).