Long story short, the guy who owned the car before me could've overheated the motor but we're not sure. Motor seemed taken care of so I wonder about it. What should I do to check if it has internal damage and if it can be saved?

 

According to your profile, you have a second generation RX-7. (A series four FC3S, to be exact.) - It helps to state which specific model RX-7 you have.


While the engine is cool and off, remove the radiator cap... Start the engine. Look for bubbles in the water/coolant as the engine runs.

Has the "low coolant" buzzer been going off? Any excessive coolant reservoir overflow??