BULLETIN NUMBER:
IB14-J-002A

IMPORTANT SERVICE
INFORMATION FOR:
 SERVICE MANAGER
 SERVICE ADVISOR
 TECHNICIAN
 PARTS DEPARTMENT
 WARRANTY PERSONNEL

ISSUE DATE:
APRIL 2020
GROUP:
ENGINE

OIL IN THE INTAKE – TURBOCHARGER INSPECTION
AFFECTED VEHICLES


2011MY – Current Isuzu N-Series Diesel Vehicles
Equipped with Diesel Particulate Filter (DPF)

This bulletin is being revised to update affected model years and procedures and
supersedes
bulletin
IB14-J-002.
Please
discard
bulletin
IB14-J-002.

INFORMATION
An investigation of returned turbochargers has identified a common occurrence of turbochargers
being replaced due to internal oil leaks when, in fact, there is no oil leak in or other fault with
the turbocharger. The perceived oil leak actually may be a normal characteristic of the closed
positive crankcase ventilation (PCV) system or some other unidentified condition.
The purpose of the closed PCV system is to keep harmful blowby gas from entering the
atmosphere. Unfortunately, blowby gas production and air intake demands do not always match
which allows some oil vapor from the crankcase to enter the intake system. As a result, this
condition may lead to an incorrect diagnosis. Oil in the intake system is common for a closed
PCV system and is not a good indicator of a turbocharger failure.
The oil seal inside the Isuzu turbocharger is a dynamic seal (not a rubber seal). Air pressure (i.e.,
boost pressure) on the compressor side and exhaust pressure on the turbine side keep the
lubricating oil inside the turbocharger center housing. A reduction in pressure on either side of the
center housing will allow oil to pass into either the intake or the exhaust side of the turbocharger.
In order to stop oil from bypassing, the source of the pressure reduction must be located and
corrected. The most common causes of this condition are a restricted air filter, incorrect
engine oil, loose intake hose clamps and/or excessive crankcase pressure.
In order to better service the customer and help prevent the unnecessary replacement of
undamaged turbochargers, we are providing the following inspection information designed to aid
the technician in properly diagnosing turbocharger concerns.
NOTE: Turbocharger replacement requires pre-authorization from ICTA; you must contact your
DSPM BEFORE replacing a turbocharger.

INSPECTION INFORMATION
Check the following items as part of normal turbocharger diagnosis.
IMPORTANT: If any of these conditions are found, the turbocharger most likely is OK and should
NOT be replaced.
A TURBOCHARGER FAILURE CAUSED BY ONE OF THESE ITEMS IS NOT A
WARRANTABLE REPAIR.


Air Filter – Should be clean without restriction. A restricted air
filter can create a vacuum condition on the intake system,
which may draw excessive oil through the closed PCV system.
Check the Filter Minder Gauge, if equipped, to determine
whether excessive inlet restriction has been recorded.
 If the air filter is restricted, replace the air filter as part
of vehicle maintenance.



Oil Level – Should not be exceeding the “MAX” level. A high
or overfilled oil level will result in high crankcase pressure
forcing excessive oil through the closed PCV system into the
air intake.
 Adjust the oil level to the correct level as part of
vehicle maintenance.



Oil Condition – Check the oil quality for deterioration (lack of
maintenance) or dilution (fuel in the oil). Poor oil quality can
lead to aeration of the oil. Aerated oil will increase crankcase
pressure forcing excessive oil through the closed PCV system
into the air intake. Check for signs of aeration (milky color).
 Replace poor quality or diluted engine oil as part of
vehicle maintenance. If diluted, find the source of
dilution and correct.



PCV System (4HK1 engine only) – Inspect the PCV hose
and the PCV oil separator for obstruction or blockage. A
blocked PCV hose will lead to increased engine crankcase
pressure and could cause a turbocharger oil leak. Please
reference service bulletin – “SB12-J-004 Air Cleaner Oil
Intrusion Prevention – Bracket and Clip” and “SB19-J-001A Oil
in the Air Cleaner – Updated Service Duct (Service Part)” for
additional information.
 Clean or replace any damaged or plugged hoses as
part of vehicle maintenance.



Noise – Listen for high-pitched noises, which can indicate air
or gas leaks. An air leak can cause unstable intake pressure
by allowing oil to leak through the turbocharger’s dynamic
seal.
 Locate, repair or replace any loose or damaged hoses
(metal, plastic or rubber) or clamps.

EXTERNAL VISUAL AND MECHANICAL INSPECTION
Any failures found during these inspections should be repaired as per the current published
Service Manual applicable to the vehicle in question.


Listen for unusual mechanical noise and watch for vibration.



General Installation - Inspect for missing or loose nuts, bolts, clamps, washers, loose
or damaged intake and exhaust manifolds and their duct clamps, damaged or
restricted oil supply and drain lines, cracked or deteriorated turbocharger housings,
external oil or coolant leakage and/or obvious heat distortion.

INTERNAL VISUAL INSPECTION
When inspecting a turbo it is normal for the turbo to have what may be deemed “excessive play”
in the turbo shaft bearings because there is no oil pressure being supplied to the turbo.
Wiggling the turbo shaft with the engine off may lead the technician to feel there is excessive play
in the turbo bearings. Some play in the turbo shaft with the engine off is normal. A technician may
also notice that pulling or pushing on the turbo shaft can cause the turbo blades to hit the housing.
This can also be normal, and should not necessarily lead to a turbo replacement.
The turbo rotates at extremely high speeds. If the bearings did have excessive wear, the turbo
blades would hit the housing. If there are no signs of the blades hitting the housing, do not replace
the turbo.
Remove the air hose, the turbocharger inlet pipe and the exhaust adapter from the compressor.
Using an inspection light, inspect the compressor and turbine wheels for evidence of foreign
object damage. If one or both of the wheels are damaged, a foreign object(s) has probably entered
through the intake or exhaust system. Be sure to identify the origin of the foreign object, as foreign
objects tend to enter the system as a result of human error or deteriorated engine/intake systems.
Repair the source of the foreign object’s entry and replace the turbocharger assembly. If NO
damage is found, inspect the radial and axial shaft play.

1. Air Hose
2. Turbocharger Inlet Pipe

Exhaust Adapter

INTERNAL RADIAL AND AXIAL INSPECTION
Perform the following radial and axial play inspections. Refer to the Turbocharger section in the
appropriate service manual. If measured play is within specification, there is no mechanical
problem with the turbocharger, there are no turbocharger-related DTCs, and the turbocharger
spins freely by hand, then it SHOULD NOT be replaced. Review the list of external visual and
mechanical inspections for other potential issues.
Wheel Shaft Axial Play
Spin the turbo shaft several times by hand before measuring, and be sure the shaft spins freely.
This will remove some excess oil from the bearings, which should provide a more accurate
measurement. Use a dial gauge to measure the wheel axial shaft play when a force of 12 N
(2.69 lb) is alternately applied to both sides of the compressor wheel.
4HK1 Axial
Measurement

Maximum Limit mm (in)

14MY – 21MY

0.13 (0.0051)

11MY – 13MY

0.09 (0.0035)

4JJ1 Axial
Measurement

Maximum Limit mm (in)

17MY – 18MY

0.13 (0.0051)

11MY – 16MY

0.09 (0.0035)

Use a dial gauge to measure the clearance between the wheel shaft and the bearing. For proper
measurement, push up and pull down on the turbine and compressor wheels at the same time.
Moving only one side or cocking of the shaft can lead to a smaller, inaccurate measurement.

4HK1 Radial
Measurement

Maximum Limit mm (in)

11MY – 21MY

0.17 (0.0067)

4JJ1 Radial
Measurement

Maximum Limit mm (in)

11MY – 18MY

0.17 (0.0067)