C-10, C-12, C-15 and C-16 Industrial Engines – Fuel Dilution of Engine Oil

Probable Causes

Leaking seals on the case of the unit injector or on the barrel of the unit injector
Leaking seals on the fuel line adapter for the cylinder head
Excessive leakage from the unit injector tip or breakage of the unit injector tip
Cracked fuel supply manifold
Leaking seal on the fuel transfer pump

Recommended Actions

Table 1
Troubleshooting Test Steps	Values	Results
1. Unit Injector Case/Barrel Seal Leak A. Check for signs of damage to the seals for the unit injectors.	Fuel Injector	Result: The unit injector seals have no damage. Proceed to Test Step 2. Result: The unit injectors seals are damaged. Repair: Replace any seals that are damaged.
2. Cylinder Head Fuel Line Adapter Seal Leak A. Check for signs of damage to the seals on the fuel line adapter for the cylinder head.	Fuel Line Adapter	Result: The fuel line adapter seals have no damage. Proceed to Test Step 3. Result: The fuel line adapter seals are damaged. Repair: Replace any seals that are damaged.
3. Unit Injector Excessive Leakage A. Check for signs of damage to the unit injector.	Fuel Injector	Result: The unit injector is not leaking and there is no damage. Proceed to Test Step 4. Result: The unit injector is leaking and there is damage. Repair: Repair or replace the unit injectors.
4. Cracked Fuel Supply Manifold A. Check for signs of damage to the fuel supply manifold.	Fuel Supply Manifold	Result: There is no damage to the fuel supply manifold. Proceed to Test Step 5. Result: There is damage to the fuel supply manifold. Repair: Repair or replace the fuel supply manifold.
5. Leaking Fuel Transfer Pump Seal A. Check to ensure that the weep hole is not plugged.	Fuel Transfer Pump	Result: The weep hole is not plugged and the fuel transfer pump seal is not leaking. STOP Result: The weep hole is plugged and the fuel transfer pump seal is leaking. Repair: Repair or replace the fuel transfer pump and the seal.