Introduction
Engine type: 6EY18ALW
Maker: YANMAR
This document briefly introduces two common issues and their solutions for reference by marine engineers.

I. Carbon Deposits, Corrosion, and Lubricating Oil Contamination in Cylinder Heads
1. Fault Description
Three YANMAR AEs on a vessel exhibited poor combustion performance. Under single-engine operation at normal load, exhaust temperature deviations between cylinders exceeded 40°C, with the highest cylinder exhaust temperature reaching 470°C.
Additionally, the lubricating oil in the sump of all three engines was contaminated at an abnormally rapid rate. The oil required replacement within less than 500 hours due to high differential pressure alarms from the self-cleaning filters.

Introduction
Engine type: 5DK-20
Maker: Anqing-Daihatsu
This model lacks an attached F.O supply pump, relying entirely on the fuel supply unit to maintain pressure.
When operating on HFO, the auxiliary engines share a common fuel supply pipeline with the main engine, with a pump discharge pressure of 0.8 MPa.
When operating on MDO, an emergency pump supplies independently, maintaining the same discharge pressure of 0.8 MPa.
A sudden drop in fuel pressure during operation can trigger load surges and blackouts, posing significant operational risks.

Introduction
Engine type: 6DC-17 
Maker: Daihatsu 
560 kW, 900 rpm.

I.Fault Symptoms
To meet the crane’s power demand, Generators No. 1 and No. 3 were operated in parallel.
the duty engineer observed abnormally low exhaust gas temperatures (EGT) in Cylinder No. 6 of AE No. 3, with deviations increasing from 30°C to 50°C over successive checks. After adjusting fuel injection, EGT temporarily normalized. However, Generator No. 3 later tripped unexpectedly, causing a total blackout.

II. Fault Diagnosis and Resolution
1. Initial Checks
Fuel injection timing: Normal.
Fuel injectors and pumps: No visible defects in pressure testing or atomization.
Fuel supply lines: No blockages detected.

Introduction
AE type: MAN B&W 6L23/30H , 720 rpm. 
Auxiliary Engine No. 4 failed to start. The specific symptom was:
Local startup attempt: Engine speed failed to reach the ignition threshold of 110 rpm, resulting in startup failure. Repeated attempts yielded the same result.

I. Fault Diagnosis
A systematic troubleshooting approach was applied to inspect the AE and its systems:
1.Fuel System Check
Fuel pressure and temperature were normal. No blockages, leaks, air bubbles, or contaminants were detected.
Conclusion: Fuel system ruled out.
2.Starting Air System Check
Air pressure and supply were sufficient. The starting motor operated normally, confirming adequate cranking speed.