Fuel dilution is limited to five sources:
1. Injection pump shaft seal
2. Fuel leaking by the rings
3. Fuel Transfer pump
4. A crack in the cylinder head from the fuel filter location to the air intake
5. Injector leakage
Use the following logic to determine the source of the oil dilution with fuel:
A worn or damaged fuel injection pump shaft seal will allow fuel to leak into the gear housing and then into the
lubricating oil pan.
The seal is designed to provide increased sealing as the pump case pressure increases. Pressure forces the lip (1)
tighter around the shaft.
A worn seal is more apt to leak during start up and shut down when case pressure is low. A worn seal cannot
easily be detected by pressurizing the pump.
The bushing (2) in the Bosch VE fuel injection pump can cause a seal leak. If the bushing is loose in the housing
it will move toward the seal raising the lip (1) and providing a leak path for fuel.
To check for such a leak, or a damaged seal (Bosch VE only), remove the fuel drain manifold connection (1) at the
pump and install a plug (2).
Remove the access cover and rotate the engine so one of the holes in the fuel injection pump gear exposes the
back gear housing.
Activate the fuel shut down valve by turning the switch to the ON position.
Use a small mirror to check for leaks while pumping the priming lever on the lift pump. If a leak is found, replace
the injection pump. The seal can be replaced by an authorized Service Center.
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.
An increase in white exhaust smoke during the first start of the day is a symptom that an injector is leaking.
An injector leak will also cause the engine to run rough and have low power.
Remove and repair or replace leaking injectors (refer to Shop Manual, 3810206, for test and repair instructions).
Perform a compression check to verify piston ring sealing (refer to the Base Engine Components Section).
There is a remote possibility for fuel to drain into the oil from the diaphram type fuel transfer pump.
For this to happen, the diaphragm in the pump would have to break and the drain hole would have to be plugged.
Another remote possibility, is a crack or porosity in the head casting could allow fuel to leak to the air intake and
on to the cylinders.
