Hummer H3. Manual — part 281

Coolant in Combustion Chamber

COOLANT IN ENGINE OIL

Coolant in Engine Oil

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.

A slower than normal cranking speed may indicate coolant entering the combustion
chamber. Refer to Engine Will Not Crank - Crankshaft Will Not Rotate.

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

Inspect by performing a Cylinder Leakage Test. During this test, excessive air
bubbles within the coolant may indicate a faulty gasket or damaged component.

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.

Warped cylinder head

Replace the cylinder head and gasket. Refer
to Cylinder Head Replacement.

Cracked cylinder head

Replace the cylinder head and gasket.

Cracked cylinder sleeve 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.

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.

2007 Hummer H3

2007 ENGINE Engine Mechanical - 3.7L - H3

ENGINE COMPRESSION TEST

Tools Required

J 38722 Compression Tester. See Special Tools.

A compression pressure test of the engine cylinders determines the condition of the rings, the
valves and the head gasket.

Test Procedure

1. Remove the air duct from the throttle control module.

2. Remove the ignition control modules.

3. Disable the fuel system.

4. Remove the spark plugs.

Inspect by performing a Cylinder Leakage Test. During this test, excessive air
bubbles within the cooling system may indicate a faulty gasket or damaged
component.

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.

Warped cylinder head

Replace the cylinder head gasket. Refer to
Cylinder Head Replacement.

Cracked cylinder head

Replace the cylinder head and gasket.

Cracked cylinder sleeve or engine block

Replace the components as required.

Cylinder head, block or manifold porosity

Replace the components as required.

Faulty sealing on engine front cover

Reseal or replace front cover.

IMPORTANT: The battery must be at or near full charge. Do not block the

throttle open.

2007 Hummer H3

2007 ENGINE Engine Mechanical - 3.7L - H3

Fig. 24: Measuring Compression Pressure
Courtesy of GENERAL MOTORS CORP.

5. Measure the engine compression, using the following procedure:

1. Firmly install J 38722 to the spark plug hole. See Special Tools.

2. Have an assistant crank the engine through at least four compression strokes in the

testing cylinder.

3. Check and record the readings on J 38722 at each stroke. See Special Tools.

4. Disconnect J 38722 . See Special Tools.

5. Repeat the compression test for each cylinder.

6. Record the compression readings from all of the cylinders. A normal reading should be

approximately 1482 kPa (215 psi).

2007 Hummer H3

2007 ENGINE Engine Mechanical - 3.7L - H3

The lowest reading should not be less than 70 percent of the highest reading.

7. The following are examples of the possible measurements:

When the compression measurement is normal, the compression builds up quickly and
evenly to the specified compression on each cylinder.

When the compression is low on the first stroke and tends to build up on the following
strokes, but does not reach the normal compression or if the compression improves
considerably with the addition of three squirts of oil, the piston rings may be the cause.

When the compression is low on the first stroke and does not build up in the following
strokes or the addition of oil does not affect the compression, the valves may be the
cause.

When the compression is low on two adjacent cylinders or coolant is present in the
crankcase, the head gasket may be the cause.

8. Install the air duct to the throttle body.

9. Install the spark plugs.

10. Enable the fuel system.

11. Install the ignition control modules.

CYLINDER LEAKAGE TEST

Tools Required

J 35667-A Cylinder Head Leakdown Tester. See Special Tools.

Test Procedure

2007 Hummer H3

2007 ENGINE Engine Mechanical - 3.7L - H3