2001 jeep grand cherokee overheated

by Judy
(alpharetta, ga)

My 2001 jeep grand cherokee overheated 1.5 hrs into a 2 hr drive. We pulled over, added coolant started driving again and had to pull over when the car lost all power. We called a tow truck and was towed to a local area mechanic. He checked out the car, said it was the the thermostat.

He said the engine was good so I had him put in a new thermostat and water pump. Drove the car back home and the next morning a sign in the car said "coolant low" so I added some. The thermostat needle stayed right in the middle but noticed the coolant bubbling in the reserve tank even though the car did not overheat.

Took it to the dealership the next day (driving there it totally overheated)and they are saying it's either a blown head gasket or a cracked head. My question, do you think the engine or the thermostat caused all this? Also if it was the engine, why would the mechanic say the engine was good and do the other work?
Thank you