I recently bought a 96 avenger with 2.5 auto. Recently the Check Engine Light comes on in the morning (but not at night), overheats sporatically, and doesn't blow heat. When I went to add in more coolant it looked really rusty.
I am hoping the dealer I bought it from is willing to fix this, but I am looking for suggestions to what it could be before I bring it to him.

Additionally, but not as important, when the overhead lights are set to "Door" and they dont come on but work when I hit the switch.

 

ill tell you this much about the door switch. either check a fuse, or the most probable is the little switches for your doors dont work, OR even a bad ground with them, pull one and check if it's rusted or a connection. just a thought as for the coolant...oil :O could be a headgasket problem. but let someone with more experience answer that one

 

Rusty looking water in the coolant suggests that tap water was used or more water than coolant was used, not to mention, the cooling system was not completely filled at some point and had air pockets. As for the heater not working, that suggests that there isn't enough coolant in the entire system. I would suggest flushing the cooling system completely and filling it up completely with 50/50 premixed coolant. While you're there also replace the thermostat because that is most likely rusted too. Before you fill the system with coolant, check to make sure the system didn't use the Orange/Red colored coolant since DCX also used that type. Look around the engine bay for a marker or sticker of some sort, if you feel confident that there isn't anything signifying that Orange/Red coolant wasn't used, then go with the green stuff. Also make sure that the coolant isn't just Orange/Red, make sure that it is rust with metal particles in it. BTW, rust with metal particles is not good.

The door switch is dirty, remove it by unscrewing the switch, spray some WD-40 while working the switch up and down. That will clean the contacts and it's ground point(s).

 

...and the dealer should have seen the coolant since they check everything over before they buy it from the original owner (god forbid that they get screwed on a car). Check your state's laws concerning lemon laws.

 

Thanks guys for the help and suggestions. I was hoping it would have just been the thermostat, but it turns out that the Water pump went.