Overheating started after replacing the alternator

Hello,

An engine can overheat due to a number of reasons.
First of all, it could be as simple as being low on coolant. It can also overheat due to a bad water pump, inoperative cooling fans, faulty radiator, having restriction in the cooling system, and of course the thermostat that you have already changed.

Did it overheat before the alternator replacement?

Do you know if the cooling fans are coming on when the engine is at operating temperature?

Take a look at this helpful guide:

https://www.2carpros.com/articles/engine-overheating-or-running-hot

Let me know what you find or if you have any questions.
Thank you.