First of all, it's very important to remember not to remove the radiator cap or any hose while the engine is still hot and under pressure; serious burns from coolant can occur.
There are more reasons your engine could be overheating than it would be realistic to discuss in this format. Everything from coolant fan failure to a bad head gasket to an incorrect radiator cap could be the source.
When talking about overheating problems on the Stratus, however, the first thing that comes to mind is the water pump. A water pump is just what it sounds like, a mechanical device, driven by a belt that pumps coolant (antifreeze) to the engine, heater core and cooling systems of your vehicle. While the water pump circulates the coolant continuously through your engine, the thermostat is what will tell it at what rate to push the coolant. The water pump consists of a main body, a flange, a main shaft, bearings, seals, an impeller and a gasket that will seal it to the engine.
When a water pump goes bad or is going bad, a couple of things can happen. First you could hear a squeaking noise or a rattle under the hood and see an increase in temperature. Second, it could leak coolant. Depending on how bad the leak is, you might see drips under the engine or you may see a large puddle. Finally, the pump can fail internally. There is a small impeller that can fail inside the pump, thereby not allowing it to pump coolant, but also not showing any of the visible symptoms, like a coolant leak or a noise.
The Dodge Stratus was available with both a four-cylinder and a six-cylinder engine. The water pump on the four cylinder engine is driven by the water pump that has a steel impeller; they are not as prone to breakage as the ones with plastic impellers. If the water pump is deemed bad on a four-cylinder engine, it is wise to also replace the timing belt since it will be off anyway.
The water pump on the six cylinder engine is behind the timing cover and is driven by the timing chain. It does have a plastic impeller and these water pumps are known to be troublesome. It is possible to find aftermarket water pumps with steel impellers; however, at this time Dodge is still making them with plastic impellers. If you have to replace the pump on a six cylinder engine, I would definitely look into finding one with a steel impeller.
Because of the difficulty level in diagnosing an overheating problem, it is probably a good idea to bring this one to a qualified mechanic. If the water pump is the source of the problem, it is a very complicated repair no matter which engine we are talking about.
It is also worthwhile to check and make sure that any parts you have replaced already were for the correct vehicle. It's a common mistake to put a radiator cap for a 2.4 liter engine on a 2.7 liter.
If you want to determine on your own if the water pump is circulating coolant, it is possible, although probably wiser to bring it to someone who is certified in engine repair.
-For the 2.0 or 2.4 liter engine, first make sure the engine is cold. Remove the radiator cap and remove a small amount of coolant. Start the engine and allow it to idle until the thermostat opens. You should be able to see coolant flowing when looking down into the filler neck. Replace the radiator cap and the removed coolant.
-For the 2.7 liter engine, start the engine and allow it to come up to temperature. You should be able to see coolant flow when you rev the engine in the coolant pressure container.
It is also possible to check the coolant flow on either engine by starting it and allowing it to come up to temperature and then squeezing the upper radiator hose, it should be hot if the coolant is flowing correctly.
If the radiator cap, thermostat and water pump have all been verified as functioning correctly, the next thing to look at would be a problem with the cooling fans, a cracked head or a bad head gasket.