Lubricating Oil Pressure
When the diagnosing lubricating system malfunctions, check all obvious items related to oil pressure, such as
gauges, high and low oil level, excessive oil contamination, and oil viscosity.
High lubricating oil pressure occurs after the engine is first started in cold weather. Cold-start oil pressure typically
will be approximately 689 to 827 kPa [1 00 to 120 psi]. If the pressure regulator plunger is operating properly, the
oil pressure is approximately 414 kPa [60 psi] when normal operating temperature is reached.
The engine will have high oil pressure at normal operating temperature if the lubricating oil pressure regulator valve
sticks in the closed position.
Check the regulator for freedom of movement. Refer toProcedure 007-029 in Section 7.
Low lubricating oil pressure (or no oil pressure) can be caused by several lubricating system-related malfunctions. To begin the investigation, determine the engine operating conditions when the low pressure was first observed. The following are conditions of low lubricating oil pressure:
• Following a service interval
• At idle only
• Operating on a steep grade
• Operating in rough seas.
High lubricating oil level can cause low oil pressure. If the oil level is high enough for the connecting rods to dip into
the oil while operating, the oil can become aerated, resulting in low oil pressure.
Low oil level will not normally appear as low oil pressure.
Typically, it will appear as an intermittent loss of oil pressure when rounding a corner or operating on a steep
grade. This condition exists when the oil level is extremely low and the suction tube can not pick up oil during all
modes of operation.
A plugged lubricating oil filter will cause a gradual loss of oil pressure by approximately 69 kPa [10 psi]. The
pressure will return to normal when the filter bypass valve opens. If not corrected, this will result in severe engine
wear, as the engine is running on unfiltered oil when the bypass valve is open.
Verify the pressure with a manual gauge to make sure the lubricating oil gauge and the sending unit are operating
correctly.
A loose lubricating oil suction tube, damaged gasket, or crack in the suction tube can cause a loss of prime for the
oil pump. The engine will have low pressure or no oil pressure during starting, followed by normal oil pressure.
A steady decrease in oil pressure over a long period can be an indication of worn bearings or excessive lubricating
oil pump wear.
Lubricating Oil Dilution
Check the condition of the lubricating oil:
• Thin, black oil is an indication of fuel in the oil
• Milky discoloration is an indication of coolant in the oil.
Coolant in the oil can be caused by:
• Expansion plugs leaking
• Oil cooler element leaking
• Damaged cylinder head or gasket
• Cracked engine block
• Casting porosity.
Since the lubricating oil cooler design does not require gaskets or seals to maintain the separation of oil and
coolant, a leaking element can allow the fluids to mix.
Refer to Procedure 007-003 in Section 7.
While operating, the oil pressure will be higher than coolant pressure. A leak in the oil cooler will show as oil
in the coolant.
However, following an engine shutdown, the residual pressure in the coolant system can cause coolant to seep
through the leak path into the oil.
If the oil cooler element ruptures, the oil pressure will force oil into the coolant system.
Oil in the coolant will be visible when the radiator cap is removed. Refer to Procedure 007-003 in Section 7.
To check for leaks, pressurize the cooling system to 140 kPa [20 psi]. With the system pressurized, remove the
following components and inspect for leaks:
• Rocker lever cover. Refer to Procedure 003-011 in Section 3. Leaks indicate a cracked cylinder head.
• Lubricating oil drain plug. Leaks indicate a damaged oil cooler, cylinder head gasket, or cracked cylinder head or block. Refer to Procedure 007-037 in Section 7.
Coolant in the lubricating oil can be caused by a damaged cylinder head gasket or cracked cylinder head or block.
Remove the cylinder head and gasket. Refer to Procedure 002-004 in Section 2.
Inspect for cracks or any other damage.
Fuel dilution of the lubricating system is generally due to the injector, but may also be due to internal damage to the
high-pressure pump.
A damaged or missing a-ring seal on the injector(s) can cause fuel dilution of the lubricating oil system. The a-ring
seal on the injector seals the injector return fuel in the internal cylinder head drilling.
Incomplete combustion in the cylinders can result in unburned fuel draining into the oil pan.
This condition can be caused by a leaking injector or reduced compression caused by inadequate piston ring
sealing.
Lubricating Oil Consumption and Leaks
Various gaskets, seals, and plugs are used to contain the lubricating oil. Most leaks can be identified during routine
inspections of the engine and vehicle.
A black light kit, Part Number 3163338, and fluorescent tracer, Part Number 3376891, must be used to verify the
source of an oil leak.
Worn or damaged seals in the turbocharger can also allow oil to leak into the charge-air cooler system and be burned
in the engine.
The condition can be verified by removing the air crossover tube or charge-air cooler tubing and looking for
oil. Refer to Procedure 010-019 in Section 10. Refer to Procedure 010-027 in Section 10.
NOTE: If the engine experiences a turbocharger malfunction or any other occasion where oil or debris is
put into the charge-air cooler, the charge-air cooler must be cleaned.
Inadequate sealing of the piston rings will result in excessive oil out of the crankcase breather system and/or
being consumed by the engine.
NOTE: Some engines are equipped with a closed crankcase breather system in which crankcase gasses are
routed to the intake air system prior to the turbocharger inlet. It is not uncommon for an engine equipped with a
closed crankcase breather system to have a residual amount of oil in the charge-air cooler plumbing.
Lubricating oil can also be lost through a worn or malfunctioning air compressor. Look for carbon build up
in the air line from the compressor to the air tank.
Also, a damaged air compressor head gasket or cylinder head gasket can allow oil to leak into the coolant or coolant
to leak into the oil during a hot shutdown.
