This bulletin applies to 2008-2010 Chevy Cobalt models. According to GM, in “rare instances,” the engine may overheat or the coolant temperature may run abxxxnormally high.
If standard 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 (secured with four bolts).
If the chain has broken, it will not be routed 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.