Head Gasket External Coolant Leak - keywords LNJ loss low overheat

This PI has been revised to delete 06 MY and update repair procedure. Please discard PIP3770B.

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

Some customers may comment about a coolant leak coming from the engine. Upon closer inspection you may find that the coolant is leaking from the head gasket. Once the cylinder head is removed you may find a small tear in the gasket about a 1/2 inch long going from a coolant passageway to the outer end of the gasket. Upon further inspection you may also see a corresponding "witness mark" on the cylinder head. Lastly, you may find spiral cutter marks on the machined surface of the cylinder block once the gasket is removed.

Engineering is currently working to identify the cause of the tear in the gasket. Please note that the mark on the cylinder head is just a mark and not a crack. Therefore replacement of the cylinder head is NOT required. Also note that the spiral cutter marks on the cylinder block machined surface are not the cause of the gasket failure and therefore can remain. Until more is known about the cause for the tear in the gasket material, replace the leaking head gasket(s) with a new gasket(s) from GMSPO. All the head gaskets (individual or in kits) currently available from GMSPO are the latest design. When replacing the head gaskets new head bolts must be used. In addition, new bolts must be used when reinstalling the intake manifold. The information in SI will be updated soon regarding the use of new intake manifold bolts.

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.