Why is our 2004 Impala over heating after installing thermostat and new radiator?

No your car is not overheating, most if not all thermostats open at 195 degrees. The average engine temp for todays cars is around 200 - 210 degrees, if it does not go over that you are fine.. just be sure you have the proper amount of water/coolant mixture in the radiator per manufacturers recommendations.

A blown head gasket or a cracked cyl head issue is first on the bad cooling system pressure jacket blowout quandary.

Could be a few things. Water pump defective thermostat cloggds radiator or heater core but not likely. Could also be your coolant temperature sensor going out. Run by autozone and grab a coolant flush kit. And to be on the safe side i would do a coolant pressure trst as well. Best of luck

The motor should come up to operating temperature with in 5 to 10 minutes of driving.

If the temp gauge fluctuates you probably have an air pocket in the cooling system yet.

Run the motor for 15 minutes with the radiator cap off to get the air out of the system.

Normal temperature for a radiator is between 195F and 220F. So it isnt overheating.

Internal combustion engines are most efficient near boiling point, that is why thermostats are fitted. If the gauge goes over that 200 mark without the cooling fan kicking in, or the engine actually overheats, you have a problem.

Check that radiator pressurisation is happening by squeezing a rubber hose when the engine is hot, DO NOT open the radiator cap. Just feel what a rubber hose feels like to squeeze when cold for later comparison. With no pressurisation (caused by a faulty radiator cap), there is not much room for the temperature to rise before boiling occurs.

wow......so many incorrect guesses.......

I will presume that you did the repair work.......you will need to look at the thermostat for 2 reasons (1) to see what temp it opens at...there will be #'s on the tip like 180, or 190, etc....and (2) to see if it was installed correctly..............some people will install the thermo backwards

that vehicle should have a thermo at either 180 degrees or 195, and here's a video for you - https://www.youtube.com/watch?v=BYMMDPSghmU

Make sure the radiator fans operate. If they don't check the fan relay and replace it if it's bad. A leaking water pump can reduce system pressure, lowering boiling point and encouraging boil-over. Make sure the radiator cap holds pressure for the same reason. The normal operating temp for your car is 200 F-210 F. You may have no problem.

So long as it stays there and doesn't go higher, or much lower, that's normal.

Most open around 190F so don't worry. Water boils at 212F at atmospheric pressure BUT pressurizing the system raises the boiling point as does mixing antifreeze with it. Modern engines are designed to run in the 200F range.