Would need to know if car was overheating before waterpump and thermostat was replaced.
Be sure the thermostat is not installed backwards.
water pump
A thermostat blocks water flow until the engine reaches operating temperature. Without a thermostat installed the engine will be very slow to warm up in cold weather and interior heat will be delayed.
In a hot water heater, a thermostat regulates the heat
sounds like you installed new thermostat upside down if that's not the problem, you have wrong or faulty new thermostat to test thermostat out of vehicle, place in pot of boiling water and watch to see if thermostat opens
because its already warmer than what your turning the heat up to.
The thermostat might be installed backwards. The thermostat will still work, but not as efficiently as if it were installed properly. It sounds like engine is still not receiving proper water flow. This is a common mistake.
Check the thermostat to see if it was installed correctly. They can get put in backwards.
Your head gaskett
if it has a plastic impeller inside water pump it may be broke or faulty thermostat .check by boiling in water till temp its suppose to open
* A water pump failure could cause this.* If the pump is turning backwards due to the serpentine belt being improperly installed* but it sounds like a bad or mis-installed head gasket would be the most probable.Another suspect: thermostat installed backwards
Are you sure the thermostat is installed correctly, or is it low on antifreeze? I would check the antifreeze level first.