Hummer H3. Manual — part 488

required.

Bent valve in the cylinder head

1. Inspect the valves and the cylinder

heads.

2. Repair or replace the components, as

required.

Seized oil pump

1. Inspect the oil pump assembly.

2. Repair or replace, as required.

Hydraulically locked cylinder

Coolant/antifreeze in the cylinder

Oil in the cylinder

Fuel in the cylinder

1. Remove the spark plugs and inspect for

fluid in the cylinder. When rotating the
engine with the spark plugs removed,
the piston, on compression stroke, will
push fluid from the combustion
chamber. Refer to Coolant in
Combustion Chamber.

2. Inspect for failed/broken head gaskets.

3. Inspect for a cracked engine block or

cylinder head.

4. Inspect for a sticking fuel injector.

5. Repair or replace the components, as

required.

Material in the cylinder

Broken valve

Broken piston rings

Piston material

Foreign material

1. Inspect the cylinder for damaged

components and/or foreign materials.

2. Repair or replace the components, as

required.

Seized crankshaft or connecting rod bearings

1. Inspect crankshaft and connecting rod

bearings.

2. Repair or replace the components, as

required.

Bent or broken connecting rod

1. Inspect the connecting rods.

2. Replace the piston and pin as an

assembly, as required.

Broken crankshaft

1. Inspect the crankshaft.

2. Repair or replace the components, as

2008 Hummer H3

2008 ENGINE Engine Mechanical - 5.3L - H3

COOLANT IN COMBUSTION CHAMBER

COOLANT IN ENGINE OIL

required.

Cause

Correction

DEFINITION: Excessive white smoke and/or coolant type odor coming from the exhaust
pipe may indicate coolant in the combustion chamber. Low coolant levels, an inoperative
cooling fan, or a faulty thermostat may lead to an overtemperature condition, which may
cause engine component damage.

1. A slower than normal cranking speed may indicate coolant entering the combustion

chamber. Refer to Engine Will Not Crank - Crankshaft Will Not Rotate.

2. Remove the spark plugs and inspect for spark plugs saturated by coolant or coolant in

the cylinder bore.

3. Inspect by performing a cylinder leak-down test. During this test, excessive air

bubbles within the coolant may indicate a faulty gasket or damaged component.

4. Inspect by performing a cylinder compression test. Two cylinders side-by-side on the

engine block, with low compression, may indicate a failed cylinder head gasket. Refer
to Engine Compression Test.

Faulty cylinder head gasket

Replace the head gasket and components, as
required. Refer to Cylinder Head Cleaning
and Inspection and Cylinder Head
Replacement - Left Side or Cylinder Head
Replacement - Right Side.

Warped cylinder head

Machine the cylinder head to the proper
flatness, if applicable and replace the cylinder
head gasket. Refer to Cylinder Head
Cleaning and Inspection.

Cracked cylinder head

Replace the cylinder head and gasket.

Cracked cylinder liner or engine block

Replace the components, as required.

Cylinder head or engine block porosity

Replace the components, as required.

Cause

Correction

DEFINITION: Foamy or discolored oil or an engine oil overfill condition may indicate
coolant entering the engine crankcase. Low coolant levels, an inoperative cooling fan, or a
faulty thermostat may lead to an overtemperature condition which may cause engine

2008 Hummer H3

2008 ENGINE Engine Mechanical - 5.3L - H3

ENGINE COMPRESSION TEST

1. Charge the battery if the battery is not fully charged.

2. Disable the ignition system.

3. Disable the fuel injection system.

4. Remove all spark plugs.

5. Turn the ignition to the ON position.

6. Depress the accelerator pedal to position the throttle plate wide open.

7. Start with the compression gage at zero and crank the engine through 4 compression strokes,

4 puffs.

8. Measure the compression for each cylinder. Record the readings.

9. If a cylinder has low compression, inject approximately 15 ml (1 tablespoon) of engine oil

component damage. Contaminated engine oil and oil filter should be changed.

1. Inspect the oil for excessive foaming or an overfill condition. Oil diluted by coolant

may not properly lubricate the crankshaft bearings and may lead to component
damage. Refer to Lower Engine Noise, Regardless of Engine Speed.

2. Inspect by performing a cylinder leak-down test. During this test, excessive air

bubbles within the cooling system may indicate a faulty gasket or damaged
component.

3. Inspect by performing a cylinder compression test. 2 cylinders side-by-side on the

engine block with low compression may indicate a failed cylinder head gasket. Refer
to Engine Compression Test.

Faulty external engine oil cooler

Replace the components, as required.

Faulty cylinder head gasket

Replace the head gasket and components, as
required. Refer to Cylinder Head Cleaning
and Inspection and Cylinder Head
Replacement - Left Side or Cylinder Head
Replacement - Right Side.

Warped cylinder head

Machine the cylinder head to proper flatness,
if applicable, and replace the cylinder head
gasket. Refer to Cylinder Head Cleaning
and Inspection.

Cracked cylinder head

Replace the cylinder head and gasket.

Cracked cylinder liner or engine block

Replace the components, as required.

Cylinder head, block, or manifold porosity

Replace the components, as required.

2008 Hummer H3

2008 ENGINE Engine Mechanical - 5.3L - H3

into the combustion chamber through the spark plug hole. Measure the compression again
and record the reading.

10. The minimum compression in any 1 cylinder should not be less than 70 percent of the

highest cylinder. No cylinder should read less than 690 kPa (100 psi). For example, if the
highest pressure in any 1 cylinder is 1 035 kPa (150 psi), the lowest allowable pressure for
any other cylinder would be 725 kPa (105 psi). (1 035 x 70% = 725) (150 x 70% = 105).

Normal - Compression builds up quickly and evenly to the specified compression for
each cylinder.

Piston Rings Leaking - Compression is low on the first stroke. Compression builds up
with the following strokes, but does not reach normal. Compression improves
considerably when you add oil.

Valves Leaking - Compression is low on the first stroke. Compression usually does not
build up on the following strokes. Compression does not improve much when you add
oil.

If 2 adjacent cylinders have lower than normal compression, and injecting oil into the
cylinders does not increase the compression, the cause may be a head gasket leaking
between the cylinders.

CYLINDER LEAKAGE TEST

Tools Required

J 35667-A Cylinder Head Leakdown Tester, or equivalent

IMPORTANT: A leakage test may be performed in order to measure

cylinder/combustion chamber leakage. High cylinder leakage may
indicate one or more of the following conditions:

Worn or burnt valves

Broken valve springs

Stuck valve lifters

Incorrect valve lash

Damaged piston

Worn piston rings

Worn or scored cylinder bore

Damaged cylinder head gasket

Cracked or damaged cylinder head

2008 Hummer H3

2008 ENGINE Engine Mechanical - 5.3L - H3