BULLETIN NUMBER:
IB16-J-002B

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

ISSUE DATE:
JULY 2020
GROUP:
ENGINE

POSSIBLE CAUSES FOR ENGINE OIL DILUTED WITH DIESEL FUEL
AFFECTED VEHICLES
 2018MY-Current Isuzu FTR
 2005MY-Current Isuzu N-Series
 2005-2010MY GMC and Chevrolet W-Series
Equipped with 4HK1 5.2L Diesel Engine
 1999-2009MY Isuzu F/H Series
 1999-2009MY GMC and Chevrolet C/T Series
Equipped with 6HK1 7.8L Diesel Engine
 2011-2018MY NPR/NPR Stripped Chassis (Reach)
Equipped with 4JJ1 3.0L Diesel Engine
This bulletin supersedes information bulletin IB16-J-002A. This bulletin is being
updated to revise Model Years, Models, and Content. Please discard previous
bulletin IB16-J-002A.
INFORMATION
Isuzu Motors Limited has analyzed failed engines and determined that engine oil diluted
with diesel fuel is a cause of some engine failures. If the engine oil level is high, the oil
may be diluted with diesel fuel. This bulletin is being issued to advise dealers of
possible reasons that engine oil may be overfull or diluted with diesel fuel.
1. Engine oil is overfilled during maintenance.
Refer to Figure 1 for correct oil level on a dipstick.

Figure 1

When refilling the engine oil, refer to the Workshop Manual (WSM) for the oil
capacity of the engine you are servicing. Fill the engine with about 80% of the oil
capacity. Start the engine to allow the oil filter to fill. Turn the engine off and allow
the oil to drain down for several minutes, then check the dipstick. Continue to add
oil as necessary to bring the level up to the full mark on the dipstick.
Note: On 2007-2010MY Models equipped with 4HK1 engines, refer to TSB
SB09-J-006, “Oil Related Misdiagnosis – Engine Oil Dipstick Calibration
Incorrect,” to ensure the correct dipstick is used.
2. Fuel tank fill and vent hoses are kinked during temporary transport or
during vehicle upfit.
If the fuel tank fill and vent hoses are kinked, a vacuum will build up inside the
fuel tank while the engine is running. This condition may cause the fuel tank to
contract, potentially blocking off the fuel return line at the bottom of the fuel tank.
This, in turn, will increase fuel pressure in the fuel return line, causing the fuel
pump seal to release fuel into the crankcase.
Refer to Figure 2 for an illustration of improperly installed and kinked fuel tank fill
and vent hoses during transport.

Figure 2

3. Restricted fuel return line
A restricted fuel return line between the engine and the fuel tank will increase fuel
pressure in the fuel return line, causing the fuel pump seal to fail, releasing fuel
into the crankcase. Check the upfit installation to ensure that a fuel return line
has not been crushed or kinked.
Inspect the fuel tank for signs of physical damage, such as dents. (See Figures 3
and 4.) If the fuel tank has been dented or crushed, the fuel return line may be
restricted from returning fuel into the tank, causing the fuel pump seal to fail
releasing fuel into the crankcase.
Indentation where impacted
tank restricted return pipe

Floor of tank is raised
from impact

Figure 3

Figure 4

4. Incorrect installation of high pressure injector lines.

Lines can become damaged if improperly handled or improperly aligned during
installation. Isuzu recommends that all high pressure fuel injection lines be
replaced any time they are removed. Please follow the applicable Workshop
Manual procedure to make certain new lines are aligned and torqued properly.
Note: Any time a high pressure fuel injector line is replaced, the oil level
should be measured and recorded before the vehicle is driven. A rise in oil
level after a repair would be an indication of a fuel leak into the crankcase.
The oil level should be rechecked after the vehicle’s normal test drive to
ensure a fuel leak into the crankcase is not occurring.
5. Leaking fuel return line gaskets under the valve cover (4HK1/6HK1 only)
If the fuel return lines have to be removed, new gaskets should be used when
reinstalling them. Refer to the applicable Workshop Manual for proper torque.