Overheated engines often cause the head to warp, resulting in a blown headgasket. If the engine blows out the coolant, you have a bad head gasket/warped head. If you're getting coolant in the oil, same thing. If one or two cylinders have very low compression, same thing.
It's not news that anyone wants to hear, but I'd check that first since it's a very common condition after an engine overheats.
If it is leaking coolant. And you changed the thermostat. I would then move to this section. Flush the radiator and the heater core. This can be done at a certified shop with a reliable mechanic.
Flush your radiator coolant and replace thermostat
You might have bad actuator that opens and closes airways.
Check the radiator for full coolant. Check the engines water pump and thermostat, as the engine coolant carries heat from the engine into the heater core.
Blown head gasket?
You could have a bad water pump causing no coolant flow, inoperable radiator fans, a coolant leak,............
The thermostat.
The coolant is pumped from the thermostat housing into the top of the radiator but not until the thermostat opens.
The function of a car thermostat is to ensure that coolant gets to the radiator when it should. It blocks the coolant from reaching the radiator when the radiator is cold, and then lets it flow once it is heated up.
The function of a car thermostat is to ensure that coolant gets to the radiator when it should. It blocks the coolant from reaching the radiator when the radiator is cold, and then lets it flow once it is heated up.
the thermostat
No. The thermostat controls the flow of water through the radiator, not the heating core. Using a thermostat with a higher temperature rating delay the opening of the thermostat (and the flow of water to the radiator) until that higher temperature is reached. This will cause the coolant to run hotter.