A South African workshop repaired combustion leakage around a diesel injector by replacing the lower sealing washer.
For a short period, the area remained clean.
Later, black carbon began building around the injector again.
Instead of replacing another washer immediately, the technicians inspected the injector seat more closely.
The lower injector seal depends on two surfaces working together:
the sealing washer and the injector seat.
If the seat has become eroded, uneven, or damaged, a new washer may not create a reliable sealing surface.
Combustion gas can then escape again.
Seat erosion should also be distinguished from incorrect sealing washer installation. An additional washer can change the injector's installed position even when the cylinder-head seat is undamaged. For a related explanation, see this injector sealing washer installation guide.
The injector was removed and the bore was cleaned.
The workshop found that the seating surface had deteriorated.
This explained why repeated washer replacement had not created a lasting repair.
The seat was restored according to the workshop repair procedure.
The injector and appropriate sealing components were then installed again.
The engine was run and the injector area monitored.
No new combustion leakage appeared during verification.
Diesel engines operating for long hours in commercial, agricultural, and industrial environments can accumulate significant deposits around injectors.
When leakage has existed for a long period, the workshop should consider whether the seat itself has been damaged rather than assuming the washer is the only issue.
This case shows why repeated injector sealing failure requires inspection of the cylinder-head seat.
Replacing the washer without correcting an eroded seating surface can allow the same fault to return.
The sealing interface must be treated as a complete system.
