No heat

My wife informed me that today our 2001 Concorde 2.7L wouldn't heat this morning. She said that after 20 minutes of driving, it finally started to blow "kinda, but not really that warm air" from the defroster vents. The antifreeze resivoir was a little low, but not by much - half a pint at the most. She also mentioned the temp gauge hovered in it's usual area, then crept up a bit, but still nowhere near the red, then suddenly dropped back down to normal. My first guess is the thermostat is sticking, hence the no heat, and the temp gauge bit was just the normal cycle of the cooling fans, amplified slightly because coolant was not displacing any heat through the heater core like it normally does.

Has anyone else had this happen on a 2.7L? Was it the thermostat or something else? I don't want to replace the t-stat on a whim because it's a whopping $30, and the entire upper intake plenum has to come off just to change it. I'm assuming the thermostat on the 2.7 is the thing front and center of the engine, four bolts holding it on (two of them shoved too far under the #%$$##@ intake to get at), the radiator/bypass line mounted to the front via an o-ring tube and 2 screws, with a bleeder valve on top. If I'm wrong about that somebody please chime In!! :)

actually, you'll hate this, the thermostat is on the left (driver's) side bank behind the alternator. You'll have to remove the alternator to gain access to two of the bolts that hold the thermostat housing in place. So, if you don't have a lift, you'll be on your back trying to replace the thermostat. It's a pain, I know, I replaced many of them when I work at a Dodge dealer. If you have no heat, and everything checks out ok under the hood, the next step would be a bad blend door not allowing the heat to be cycled properly. Since the mode doors are electronically operated by motors, you can pull up any fault codes that the BCM may have stored. To access those codes, turn your fan on high, on defrost, have the thermostat in full code and press the EBL (rear window defroster) for about 5 seconds until you hear a chime, it's now in diagnostic mode. Look on your odometer display and you'll see codes appearing (24, 28, etc.). I can't think of all the codes and as to what they mean at this time, but give me a day or so and I can get those for you.

At least I won't have to take off the intake plenum :) You said you've replaced a lot of them, so I'm confident it is the thermostat that's the problem.

My daughter had the same problem.
Look at this site under "no heat from vents":
http://experts.about.com/q/807/

Turns out, just like the linked article above, the system had an air bubble. I bled the system via the valve on the radiator inlet, and now the heat is working better then ever. In fact, if you turn the blend control up past 60% warm, it'll cook you right out of the car!!!! Good thing I read that before I pulled the alternator off.....