[jb92563]

Did you follow the procedure to properly get all the air out of the coolant system?

Car shops charge ~$90 to do this using their coolant vacuum systems to ensure no air bubbles.

Just filling it via the coolant fill tank cap will not do the trick and cause more overheating and premature water pump failure.

Also, you need to use distilled water with the coolant concentrate if doing it yourself and not using a premixed type.

For the cost of equipment to do the jobs right its best just to have the car shop do this for you in this case, unless you already have the proper equipment.

Update - Sounds like maybe there is a way to do it yourself without a vacuum system.
Pelican Technical Article: Boxster Coolant Replacement / Boxster Coolant Flush - 986 / 987