I recently had the starter replaced and my radiator flushed. Later on, my engine started running sluggish and hesitating. The radiator fluid also burst out of the reservoir and now the engine is overheating.
It sounds like there may be some air in the coolant system. After they drain the coolant and put in new coolant they may not have bled the air out of the engine. What needs to be done is take the radiator cap off and run the engine turn the heat on and keep filling the radiator up until there are no air bubbles coming out of the system and the coolant level no longer goes down. I would recommend a technician from YourMechanic come out and inspect your overheating problem and replace the head gasket, if necessary.