i have a 2000 durango with almost 200k miles and its overheating. replaced thermostat and electric fan and its still over heating. I don't know what to do next. I have the 5.2 L only 2wd. thermostat was non existent since I bought it a year ago. I've never had this problem before and I live in florida with this heat and i don't know why it happened now when its cooler out but not at all last summer. I had just found this out when I went to put a new one in it. water pump seems to be pumping cause its fine at idle, but soon as I start driving it over heats

 

are you loosing coolant? is the radiator partially clogged? (you can check this with a IR thermometer, or a FLIR camera if you have access to one)

 

not losing any coolant.. the radiator being stopped up I don't know. and I don't have access to either of those

 

You can pick up the IR thermometer from the parts store pretty cheap...... the camera, on the other hand, is likely terribly expensive.

 

i don't know if this makes a difference or not but when i put water straight into the block where the thermostat goes, the engine wont over heat.. it'll get to 240 but it will go back down to like 130 long as i keep moving at a good pace

 

An air pocket in the cooling system will do that......

 

 

well if your not loosing coolant how is there any room in the cooling system for you to put water in there? that should remain FULL unless you have a leak somewhere.

if you are able to add coolant here without removing any, and have no external leaks you have an internal leak, most likely a headgasket.