95 Dodge Avenger 2.5L V6 ES, I had to replace the a radiator hose and the thermostat and I flushed the coolant. Since then the car was overheating and it looked that it takes forever to warm up but not lately. The coolant overflow bottle was filled over the maximum limit and I drained some fluid to take it to the middle between the minimum and the maximum. That solved the overheating, but before the car used to warm up in less than 5 minutes. Now, what I get it's cold air or warm from the vents even when the car is hot. I replaced the thermostat with the oem one 180 degrees fahrenheit and the thermostat it is not locked open. It works well and the radiator fan works ok too. I wonder what the problem might be. I also replaced the coolant temperature sensor and the gauge looks to be working fine.

 

It is possible that you have a defective thermostat. Also you may have clogged your heater core when you flushed the radiator. You may have to backflush your heater core.

 

The possibility exists but this is a brand new thermostat. I think there is a big likelihood of the heater core being clogged. I have this car since 2005 and I never replaced it. Another thing I believe it could be is that I am using Dexcool (the orange antifreeze) fifty fifty, because it is not as aggressive to the engine block as the green antifreeze. I am going to have to replace the heater core for a new one. Is there any way to know if the heater core is clogged without having to take it out of the vehicle? Thank you,

 

Get the car up to normal temp and check for a temp differential between the heater hoses. Get one of those infrared trigger thermometers. They're cheap at Harbor Freight. You may be able to take the hoses off and backflush it back and forth with a garden hose...BUT you may also open a pinhole doing that if it's really bad.