Chevrolet Silverado / GMC Sierra. Service manual — part 12

OIL LEAK DIAGNOSIS

Step

Action

Yes

No

IMPORTANT:

You can repair most fluid leaks by first visually locating the leak, repairing or replacing the
component, or by resealing the gasket surface. Once the leak is identified, determine the cause of
the leak. Repair the cause of the leak as well as the leak itself.

1

1. Operate the vehicle until it reaches normal

operating temperature.

2. Park the vehicle on a level surface, over a

large sheet of paper or other clean surface.

3. Wait 15 minutes.

4. Inspect for drippings.

Are drippings present?

Go to Step 2

System OK

2

Can you identify the type of fluid and the
approximate location of the leak?

Go to Step 10

Go to Step 3

3

1. Visually inspect the suspected area. Use a

small mirror to assist in looking at hard to
see areas.

2. Inspect for leaks at the following locations:

Sealing surfaces

Fittings

Cracked or damaged components

Can you identify the type of fluid and the
approximate location of the leak?

Go to Step 10

Go to Step 4

4

1. Completely clean the entire engine and

surrounding components.

2. Operate the vehicle for several kilometers,

miles, at normal operating temperature and
at varying speeds.

3. Park the vehicle on a level surface, over a

large sheet of paper or other clean surface.

4. Wait 15 minutes.

5. Identify the type of fluid, and the

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.3L - Sierra & Silverado

approximate location of the leak.

Can you identify the type of fluid and the
approximate location of the leak?

Go to Step 10

Go to Step 5

5

1. Visually inspect the suspected area. Use a

small mirror to assist in looking at hard to
see areas.

2. Inspect for leaks at the following locations:

Sealing surfaces

Fittings

Cracked or damaged components

Can you identify the type of fluid and the
approximate location of the leak?

Go to Step 10

Go to Step 6

6

1. Completely clean the entire engine and

surrounding components.

2. Apply an aerosol-type powder, baby

powder, foot powder, etc., to the suspected
area.

3. Operate the vehicle for several kilometers,

miles, at normal operating temperature and
at varying speeds.

4. Identify the type of fluid, and the

approximate location of the leak, from the
discolorations in the powder surface.

Can you identify the type of fluid and the
approximate location of the leak?

Go to Step 10

Go to Step 7

7

1. Visually inspect the suspected area. Use a

small mirror to assist in looking at hard to
see areas.

2. Inspect for leaks at the following locations:

Sealing surfaces

Fittings

Cracked or damaged components

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.3L - Sierra & Silverado

Can you identify the type of fluid and the
approximate location of the leak?

Go to Step 10

Go to Step 8

8

Use the J 28428-E high intensity black light kit
in order to identify the type of fluid, and the
approximate location of the leak. Refer to the
manufacturer's instructions when using the tool.
Can you identify the type of fluid and the
approximate location of the leak?

Go to Step 10

Go to Step 9

9

1. Visually inspect the suspected area. Use a

small mirror to assist in looking at hard to
see areas.

2. Inspect for leaks at the following locations:

Sealing surfaces

Fittings

Cracked or damaged components

Can you identify the type of fluid and the
approximate location of the leak?

Go to Step 10

System OK

10

1. Inspect the engine for mechanical damage.

Special attention should be shown to the
following areas:

Higher than recommended fluid levels

Higher than recommended fluid
pressures

Plugged or malfunctioning fluid filters
or pressure bypass valves

Plugged or malfunctioning engine
ventilation system

Improperly tightened or damaged
fasteners

Cracked or porous components

Improper sealants or gaskets, where
required

Improper sealant or gasket installation

Damaged or worn gaskets or seals

Damaged or worn sealing surfaces

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.3L - Sierra & Silverado

CRANKCASE VENTILATION SYSTEM INSPECTION/DIAGNOSIS

Results Of Incorrect Operation

A plugged positive crankcase ventilation (PCV) orifice or hose may cause the following
conditions:

Rough idle

Stalling or slow idle speed

Oil leaks

Oil in air cleaner

Sludge in engine

A leaking PCV orifice or hose may cause the following conditions:

Rough idle

Stalling

High idle speed

Functional Check

With these systems, any blow-by in excess of the system capacity, from a badly worn engine,
sustained heavy load, etc., is exhausted into the air cleaner and is drawn into the engine.

Proper operation of the crankcase ventilation system depends upon a sealed engine. If oil slugging
or dilution is noted and the crankcase ventilation system is functioning properly, check the engine
for a possible cause. Correct any problems.

If an engine is idling rough, inspect for a clogged PCV orifice, a dirty vent filter, air cleaner
element, or plugged hose. Replace as required. Use the following procedure:

1. Remove the PCV hose from the rocker arm cover.

2. Operate the engine at idle.

2. Inspect the engine for customer

modifications.

Is there mechanical damage, or customer
modifications to the engine?

Go to Step 11

System OK

11

Repair or replace all damaged or modified
components.
Does the engine still leak oil?

Go to Step 1

System OK

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.3L - Sierra & Silverado