Hummer H2. Manual - part 1698

COOLANT IN ENGINE OIL 

Coolant in Engine Oil 

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 the spark plugs.  

head

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 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. 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 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 or Cylinder 
Head Replacement - Right .

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.

 

2004 Hummer H2 

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2

  

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 gauge at zero and crank the engine through four compression strokes, four 

puffs.  

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

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

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

10. The minimum compression in any one 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 one 
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). 

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

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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.  

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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.  

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If two 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. See Special Tools and Equipment . 

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: 

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Worn or burnt valves  

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Broken valve springs  

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Stuck valve lifters  

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Incorrect valve lash  

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Damaged piston  

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Worn piston rings  

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Worn or scored cylinder bore  

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Damaged cylinder head gasket  

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Cracked or damaged cylinder head  

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Cracked or damaged engine block  

 

2004 Hummer H2 

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2

  

1. Disconnect the battery ground negative cable.  

2. Remove the spark plugs. Refer to Spark Plug Replacement in Engine Controls - 6.0L.  

3. Rotate the crankshaft to place the piston in the cylinder being tested at top dead center (TDC) of the 

compression stroke.  

4. Install the J 35667-A or equivalent. See Special Tools and Equipment . 

5. Apply shop air pressure to the J 35667-A and adjust according to the manufacturers instructions. See 

Special Tools and Equipment .  

6. Record the cylinder leakage value. Cylinder leakage that exceeds 25 percent is considered excessive and 

may require component service. In excessive leakage situations, inspect for the following conditions: 

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Air leakage noise at the throttle body or air inlet hose that may indicate a worn or burnt intake 
valve or a broken valve spring.  

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Air leakage noise at the exhaust system tailpipe that may indicate a worn or burnt exhaust valve or 
a broken valve spring.  

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Air leakage noise from the crankcase, oil level indicator tube, or oil fill tube that may indicate worn 
piston rings, a damaged piston, a worn or scored cylinder bore, a damaged engine block or a 
damaged cylinder head.  

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Air bubbles in the cooling system may indicate a damaged cylinder head or a damaged cylinder 
head gasket.  

7. Perform the leakage test on the remaining cylinders and record the values.  

OIL CONSUMPTION DIAGNOSIS 

Oil Consumption Diagnosis 

CAUTION: Refer to Battery Disconnect Caution in Cautions and Notices.

IMPORTANT: It may be necessary to hold the crankshaft balancer bolt to prevent the 

crankshaft from rotating.

Checks

Causes

Excessive oil consumption, not due to leaks, is the use of 1 L (1 qt) or more of engine oil within 3 200 
kilometers (2,000 miles).
Preliminary The causes of excessive oil consumption may include the following conditions: 

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External oil leaks 

Refer to Oil Leak Diagnosis . 

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Incorrect oil level or improper reading of the oil level indicator 

With the vehicle on a level surface, run the engine for a few minutes, allow adequate 
drain down time, 2-3 minutes, and check for the correct engine oil level. 

 

2004 Hummer H2 

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2

  

OIL PRESSURE DIAGNOSIS AND TESTING 

Tools Required 

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J 21867 Pressure Gauge. See Special Tools and Equipment .  

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J 42907 Oil Pressure Testing Tool  

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Improper oil viscosity 

Refer to the vehicle owners manual and use the recommended SAE grade and 
viscosity for the prevailing temperatures. 

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Continuous high speed driving and/or severe usage  

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Crankcase ventilation system restrictions or malfunctioning components  

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Worn valve guides and/or valve stems  

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Worn or improperly installed valve stem oil seals  

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Piston rings broken, worn, or not seated properly 

Allow adequate time for the rings to seat. 

Replace worn piston rings as necessary. 

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Piston and rings improperly installed or not fitted to the cylinder bore  

 

2004 Hummer H2 

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2