Coolant Leak - keywords cup engine expansion freeze missing plug

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Some owners may comment about a coolant leak coming from the engine compartment. Upon inspection you may find that an expansion (freeze) cup plug may be missing from the rear side of the engine block. On Lucerne models you may find that the leak is very small and coming from the expansion plug on the front side of the engine block near cylinders 1 and 3)

For Leaking Expansion Plugs:

On Lucerne models with a small leak coming from the expansion plug on the "FRONT" side of the engine block, drain the coolant and remove the expansion plug. Check the hole in the block for any defects and then apply sealer (e.g. RTV) around the perimeter of a new expansion plug and install. Refill the cooling system and pressure test for leaks.

For Missing Expansion Plugs:

Do not attempt to install a new expansion plug. Instead you must contact GM TAC to start a case and TAC will advise of repair procedure at this time.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.