Wierd heater/temp guage actions

[mgburton]

Yesterday when I got home from work, I noticed some antifreeze on the frame of my 2000 Durango Sport (viewed from the wheel well)(4.7l 4X4). I popped the hood, and it looks like the antifreeze is coming from a little downspout on the overflow reservoir where the cap is. This morning, I was sitting in the parking lot with the engine running and the heater going full blast. I noticed that I was freezing, and looked over at the temperature guage. It was about 3/4 of the way up. It usually NEVER rises above a 1/4. I drove around to a few auto parts stores, and when I first started the engine, the air would be cool. As I drove, it would get hot again, but when I stopped, it would cool back down. Not cold, but just warm. Drove it home about 80 miles with the temp guage reading between 1/4 and 1/2 the way up. Talked to a few people, and they said that they thought it was probably the thermostat. What do you guys think. If it is the thermostat, it appears that it is located on the bottom of the engine. Can I swap it out from below, or do I have to start taking the engine apart to get to it. Thanks!!!

[mgburton]

Replaced the thermostat, now no heat whatsoever, and the temp guage is climbing over the 1/2 way mark. A small amount of coolant leaked out when I replaced the thermostat. The reading in the tank still says full, so I didn't add any.

[mgburton]

Here is the latest. Took the Durango around the block one more time. Heat is working better now. Temp not rising as high. Opened the overflow and noticed that the fluid level was way down. It was full before. Don't know if this is due to the fluid lost during the thermostat change, or due to the new thermostat working. I didn't lose much when I changed out the thermostat. Topped it off with a gallon of coolant. Working close to what it was before all this happened. Temperature fluctuates some, before it didn't at all. I tested the old thermostat with a pot of water and a thermometer. It opened at 210 degrees.
The working temp of the Durango was around 170 before. Does this sound like the problem? Any and all thoughts are welcome.

[BleedDodge]

I think you have a good thermostat in it now, and you've been low on water all along. You fill the water in the rad and not the overflow.

You should be fine now that you have a new thermostat. Just make sure you have water in there.