Chevrolet Silverado / GMC Sierra. Service manual — part 378

Fig. 506: Inspecting Intake Manifold Cylinder Head Deck For Warpage
Courtesy of GENERAL MOTORS CORP.

2. Inspect the intake manifold cylinder head deck for warpage.

1. Locate a straight edge across the intake manifold cylinder head deck surface.

Position the straight edge across a minimum of two runner port openings.

2. Insert a feeler gage between the intake manifold and the straight edge.

An intake manifold with warpage in excess of 3 mm (0.118 in) over a 200 mm (7.87

2008 Hummer H2

2008 ENGINE Engine Mechanical - 6.2L - H2

in) area is warped and should be replaced.

EXHAUST MANIFOLD CLEANING AND INSPECTION

Fig. 507: Exhaust Manifold
Courtesy of GENERAL MOTORS CORP.

IMPORTANT: Do not use the exhaust manifold-to-cylinder head gaskets

again. Upon installation of the exhaust manifold, install a
NEW gasket. An improperly installed gasket or leaking
exhaust system may affect on-board diagnostics (OBD) II
system performance.

2008 Hummer H2

2008 ENGINE Engine Mechanical - 6.2L - H2

1. Clean the exhaust manifold (600) and heat shield (603) in solvent.

2. Dry the exhaust manifold with compressed air.

3. Inspect the exhaust manifold-to-cylinder head gasket surface for excessive scratches or

gouging.

4. Inspect for a loose, damaged, or cracked heat shield (603).

5. Inspect the studs (605) for damaged threads.

Fig. 508: Measuring Exhaust Manifold To Cylinder Head Surface For Warpage
Courtesy of GENERAL MOTORS CORP.

6. Use a straight edge and a feeler gage and measure the exhaust manifold cylinder head deck

for warpage.

CAUTION: Refer to Safety Glasses Caution .

2008 Hummer H2

2008 ENGINE Engine Mechanical - 6.2L - H2

An exhaust manifold deck with warpage in excess of 0.25 mm (0.01 in) within the 2 front or
2 rear runners or 0.5 mm (0.02 in) overall, may cause an exhaust leak and may affect OBD
II system performance. Exhaust manifolds not within specifications must be replaced.

ENGINE COOLANT AIR BLEED PIPE AND HOLE COVER CLEANING AND INSPECTION

Fig. 509: View Of Coolant Air Bleed Pipe Seal
Courtesy of GENERAL MOTORS CORP.

IMPORTANT: Do not use the engine coolant air bleed pipe and cover seals

2008 Hummer H2

2008 ENGINE Engine Mechanical - 6.2L - H2