In “rare instances,” 2012 Buick Regal vehicles equipped with L61, LE5, LEA, LAF, LHU, LNF or LSJ engines may exhibit engine overheating or coolant temperatures that are abnormally high.
If service manual diagnostics do not lead to a repair, inspect for a broken water pump/balance shaft chain by removing the water pump cover plate found on the engine front cover (remove four bolts).
If the chain has broken, it will not be around the water pump gear when looking through the front cover opening, and the water pump drive gear can be turned by hand.
Inspect the water pump gear for damage and replace as needed. Replace the water pump/balance shaft chain and tensioner.