If your Avenger is running a little warm, between the 1/2 and 3/4 marks, change out BOTH of your thermostats immediately. With 2, yes two t-stats and only one heat sensor for the 2 different cooling loops, you could have a bad overheating issue and warp your head, burn your head gasket. Even if it only looks a little warm, the other t-stat and cooling loop could be having a bad failure. Its very quick and east to replace them. Both are accessible in the same area next to the airbox for your intake. Flush and refresh your coolant while you're at it.

Google for some videos on it. The smaller one against the block can be a little harder to get, the 3 bolts come out and it will move enough on the back of it to let you at the t-stat. The larger one is in the connection from the main line on top from your radiator to the engine. 2 bolts, very easy. Just pul out the air box for a little working room.

After you make the repair, check your overflow bottle and the radiator level before you drive much, make sure its drawing back from the overflow and keeping the cooling system full. If it's not, change the radiator cap and check again for a few days. If its still not drawing back, you probably have a bad head gasket and possibly warped head already. You'll probably want to take it to a shop unless you like working on motors.

The motor is supposed to be easier to work on, but any time you deal with timing chains it's a pain in the butt.

At least its not the dual overhead cam engine in a Durango I had! That was the worse engine I ever worked on.