I have a 2005 2.4L sedan stratus that starts to overheat after driving for about 30 minutes. It appears that some of the coolant flows into the overflow tank and when I get into a stop-n-go traffic, the engine doesn't cool off even with the fan running. I've replaced the radiator (after market), water pump (after market), heater core, thermostat and housing (OEM), radiator cap (OEM), temp sensor, hoses and am still having the problem. The coolant is flowing while idling and is clean. The engine cools once the car starts moving but after travelling 200 miles or so, there's not enough coolant in the cooling system to cool the engine and I need to stop the car and pump the coolant from the overflow tank back into the radiator. I have checked the transmission and oil fluid levels and they are fine and clean. There are no leaks and the coolant level is at the rim when I remove the radiator cap with a cold engine (i.e. the coolant from the overflow tank is sucked back into the radiator when the engine cools) Does anyone have any ideas what the problem could be? Is it possible that the aftermarket water pump is not providing sufficient circulation while driving causing the coolant to overheat and flow into the overflow tank?