Manufacturer communication — 2006 GMC YUKON DENALI XL

• Applies to 2001-2006 GMC Envoy, Jimmy, Sierra and Yukon models, among other listed GM models, with the 4.8L, 5.3L or 5.7L VORTEC GEN III, GEN IV V8 engine.

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  2001-2006 GMC Envoy, Jimmy, Sierra, Yukon Models 2001-2004 Oldsmobile Bravada 1998-2002 Pontiac Firebird 2005-2006 Saab 9-7X with 4.8L, 5.3L, or 5.7L VORTEC® GEN III, GEN IV V8 Engine

• Some vehicles may experience a gradual coolant loss over time.

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  Some vehicles may experience a gradual coolant loss over time.

Possible causes

• A very low percentage of cylinder heads manufactured with an embossed Castech logo may develop a porosity crack in a very specific area.

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  A very low percentage of cylinder head(s) manufactured with an embossed Castech logo may develop a porosity crack in a very specific area.

Steps to confirm (in the document’s order)

1. Check whether the head is a Castech casting by looking for the casting logo on top of the intake port, under the rocker arm support rail and in the spring deck cavity portion of the cylinder head.

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   This can be accomplished by inspecting for their casting logo located on top of the intake port, under the rocker arm support rail and in the spring deck cavity portion of the cylinder head.

2. If the head is a Castech casting, inspect the area around the five oil drain holes for witness marks indicating coolant seepage over time.

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   If the cylinder head(s) is a Castech casting (1), inspect the area around the five oil drain holes for witness marks indicating coolant seepage over time (2).

3. The crack can be in any of the five cylinder head oil drains and shows as a clean or shiny area on an otherwise stained surface.

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   The crack location can be found in any of the five-cylinder head(s) oil drains. This can be seen as a clean or shiny area, on an otherwise stained surface (1).

4. Pressurizing the cooling system at this time may reveal coolant, air, or a combination weeping in the described area.

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   Pressurizing the cooling system at this time may reveal coolant, air, or a combination, weeping in the described area.

Repair

• If inspection reveals evidence of coolant witness marks, replace the entire cylinder head assembly.

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  If inspection reveals evidence of coolant witness marks (1), replace the entire cylinder head(s) assembly.

Caution

• If the cylinder heads are not a Castech casting, follow normal diagnostic procedures in SI to determine the cause of the coolant loss.

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  If the cylinder head(s) are Not a Castech casting, follow normal diagnostic procedures in SI to determine the cause of the coolant loss.

• If no evidence of coolant loss is found on inspection of Castech casting cylinder heads, follow normal diagnostic procedures in SI to determine the cause of the coolant loss.

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  If No evidence of coolant loss is found on inspection of Castech casting cylinder head(s), follow normal diagnostic procedures in SI to determine the cause of the coolant loss.