Diesel engine fault diagnosis primarily involves monitoring the operating status of the diesel engine and its auxiliary systems to determine the equipment’s operating condition. When abnormalities occur, the causes of the fault are analyzed, the development trend of the fault is predicted, and corresponding maintenance solutions are formulated.
During ship navigation, marine diesel engines frequently experience faults such as abnormal starting, abnormal vibration, runaway, surging, abnormal noises, and sudden shutdowns. Among these, abnormal noises are often caused by internal structural faults and are typical precursors to major malfunctions, posing significant safety hazards and requiring priority investigation and handling. While normal operation of a diesel engine generates inherent conventional noises from mechanical, aerodynamic, combustion, and electromagnetic sources, this paper focuses on the study of unconventional abnormal noise faults occurring in diesel engines during ship navigation.
This paper takes an abnormal noise fault in a marine diesel engine during navigation as the research object, analyzes its fault mechanism and causes, and summarizes fault diagnosis and maintenance methods, which can provide a reference for the diagnosis and maintenance of similar faults in marine diesel engines.
I. Fault Overview
A vessel equipped with a Cummins diesel engine experienced a sudden abnormal noise malfunction after 2.5 hours of continuous sailing. Upon the occurrence of the malfunction, the engine room mechanics immediately reported it to the bridge. The operators immediately initiated emergency braking and began a comprehensive troubleshooting process.
Analysis of the equipment operation log data revealed that from 11:25:21 to 11:25:30 on July 25th, for a total of 10 seconds, the diesel engine speed fluctuated continuously between 1600 and 1800 r/min, indicating extremely unstable operating conditions. From 11:25:31 to 11:25:42, within 11 seconds after the emergency braking, the diesel engine speed gradually decreased until it stopped.
Preliminary on-site investigation results showed that the abnormal diesel engine power performance and the continuous “ticking” noise occurred simultaneously, while the equipment’s water and oil temperatures showed a gradual upward trend. An overall visual inspection revealed no coolant or lubricating oil leaks. All connecting bolts and joints were securely fastened, and the drive belt showed no signs of looseness, slippage, or breakage. The diesel engine emitted no black smoke during operation.
The core performance parameters of the Cummins diesel engine used in this study are shown in Table 1.
Table 1 Core Performance Parameters of Cummins Diesel Engines | |||||
| Item | Bore x Stroke / inch | Displacement / L | Number of Cylinders | Rated Engine Power / hp | Rated Engine Speed / (r·min⁻¹) |
| Value | 5-1/2X6 | 855 | 6 | 400 | 2100 |
II. Troubleshooting
Abnormal noises in marine diesel engines often originate from damage to internal components such as crankshaft bearings, connecting rod bearings, pistons, and piston pins, or from abnormal fuel combustion. Based on the initial troubleshooting results, the diesel engine was not producing black smoke, which preliminarily rules out abnormal combustion as the cause of the malfunction. A more in-depth investigation is needed to determine the specific cause of the malfunction.
This troubleshooting strictly followed the principles of prioritizing primary components, overall systems, and simpler components over more complex ones. A comprehensive fault detection was conducted on the diesel engine’s internal structure, operating conditions, fuel system, cooling system, intake system, and lubrication system.
2.1 Diesel Engine Disassembly and Inspection Results
The faulty diesel engine was disassembled and inspected (see right figure). After disassembly, the internal condition of the engine was observed. Scoring was found to be present to varying degrees on the cylinder walls of cylinders 1-6. The scoring on cylinders 1 and 2 was the most significant, while the damage to cylinders 3-6 was relatively minor, consistent with typical characteristics of diesel engine cylinder scoring. Therefore, it can be determined that the abnormal noise and power malfunction were caused by diesel engine cylinder scoring.
The faulty diesel engine was disassembled and inspected (see Figure 1 on the right). After disassembly, the condition of the cylinder walls was observed, and varying degrees of scoring were found on the walls of cylinders 1 to 6. Cylinders 1 and 2 showed the most obvious scoring damage, while cylinders 3 to 6 showed relatively less damage. The overall fault characteristics were highly consistent with typical diesel engine cylinder scoring faults. Therefore, it can be determined that the root cause of the abnormal noise and power loss in this diesel engine was cylinder scoring (see Figure 2 on the right).
Cylinder scoring in diesel engines is a relatively common and serious mechanical failure, mainly caused by abnormal friction between the piston rings and cylinder liner. This failure results in scratches on the surfaces of the cylinder liner and piston rings, damaging the sealing performance between the piston and cylinder liner, leading to problems such as reduced diesel engine power and difficulty starting. In severe cases, it can damage core components such as the piston and crankshaft, even causing the entire engine to be scrapped and resulting in navigational safety accidents. The following section will further analyze the specific causes of this diesel engine cylinder scoring failure.
A special disassembly and inspection was conducted on cylinders 1 and 2, which are prone to failure, and their corresponding piston assemblies. The results showed that the combustion chamber was clean and free of debris, the piston and valve structures were intact and undamaged, and there was no foreign object accumulation in the cylinder head area, ruling out foreign objects entering the combustion chamber as the cause of cylinder scoring. Simultaneously, the piston nozzle was inspected and found to be structurally intact, with unobstructed internal channels and normal fuel injection operation. Therefore, the possibility of insufficient cooling of the friction pair due to piston nozzle blockage was also ruled out.
2.2 Troubleshooting of Diesel Engine Abnormalities
The ship’s voyage log was reviewed. Since the last major overhaul, the diesel engine had accumulated less than 500 hours of operation, with the longest single voyage not exceeding 4 hours. Daily start-up, preheating, operation, and shutdown procedures strictly followed maintenance guidelines, with no records of violations. During the voyage in question, the equipment was preheated for 30 minutes, the diesel engine speed was consistently maintained below 1800 rpm, and the continuous voyage duration did not exceed 3 hours. Overall, the operating conditions were compliant and the operation was in accordance with regulations. Based on the above findings, the possibility of improper human operation causing the diesel engine cylinder scoring failure can be ruled out.
2.3 Fuel System Inspection
The Cummins diesel engine fuel system used in this voyage mainly consists of a fuel pump, inlet and outlet fuel lines, fuel passages, fuel filter, and fuel injectors. Qualified #0 diesel fuel was used throughout the voyage, and inspection revealed no quality issues such as deterioration or excessive impurities. According to the voyage log, fuel pressure and fuel consumption rate remained within standard ranges during equipment operation. After disassembly, further specialized testing was conducted on the fuel filter’s filtration efficiency, the fuel pump’s fuel supply uniformity, and the fuel injector atomization quality; all indicators met operational standards. The fuel filter was free of water, solid deposits, or other contaminants, and the inlet and outlet fuel lines were airtight, with no leaks or blockages. In conclusion, the possibility of a fuel system malfunction causing the cylinder scoring issue can be ruled out.
2.4 Cooling System Inspection
The Cummins diesel engine’s cooling system mainly consists of a water pump, cooler, coolant filter, and associated piping, relying on a centrifugal water pump for coolant circulation and heat dissipation. A comprehensive on-site inspection of the cooling system revealed that all cooling pipes were airtight, without damage, cracks, blockages, or leaks; the coolant level remained within the standard operating range, the system circulation was stable, and heat dissipation and absorption performance were normal, ruling out the possibility of cooling system malfunctions causing engine cylinder scoring.
2.5 Air System Inspection
Diesel engine combustion requires a sufficient air supply; abnormal air system operation can severely affect the combustion and operating status of the equipment. The engine’s air system comprises two main modules: intake and exhaust. Core components include the air filter, intake and exhaust pipes, and intercooler. A complete inspection of the entire engine showed that all air system connections were properly sealed, the intake and exhaust pipes were undamaged and leak-free, the intercooler was functioning normally, and the overall system showed no abnormalities. Therefore, the possibility of an air system malfunction causing engine cylinder scoring can be ruled out.
2.6 Lubrication System Inspection
The lubrication system of this Cummins diesel engine mainly includes core components such as a lubricating oil pump with a pressure regulator, an oil filter, lubrication lines, an oil cooler, and oil nozzles. The equipment uses a pressure lubrication method, with a gear-type lubricating oil pump providing lubrication pressure and a pressure regulator stabilizing the oil working pressure. The filter and screen filter impurities in the lubricating oil, while the oil cooler controls the lubricating oil temperature to ensure stable operation of the lubrication system. This diesel engine uses Cummins special engine oil throughout, and the oil compatibility meets the equipment’s operating requirements.
- Lubrication Pipeline Inspection: The sealing and continuity of the entire lubrication pipeline were tested. The results showed that the lubrication pipeline had good sealing performance, with no damage, leakage, or water ingress. The pipeline was unobstructed and free of foreign matter accumulation, ruling out the possibility of lubrication pipeline failure leading to oil supply failure and subsequent cylinder scoring.
- Oil Filter Inspection: The oil filter and internal filter screen were disassembled and inspected. A small amount of scale was found on the filter element surface, but no hard solid impurities such as metal shavings or sand particles were detected. The oil cleanliness on the filter outlet side was good. Analysis showed that the small amount of scale was a colloidal deposit formed by the oxidation of the lubricating oil during long-term high-temperature operation. This deposit was effectively intercepted by the filter element and did not enter the friction pairs of the equipment, thus not having a substantial impact on the operation of the diesel engine.
- Lubricating Oil Performance Index Inspection
To further investigate the cause of the malfunction, a sample of the diesel engine’s oil pan lubricating oil was collected on-site for performance testing (see left image). Visual observation revealed that the lubricating oil was dark black, initially indicating oil deterioration. Subsequent testing of key indicators such as water content, kinematic viscosity, and flash point showed that while the flash point met standard requirements, the water content exceeded the 0.5% threshold; the high-temperature kinematic viscosity was only 10 mm²/s, below the normal operating range of 12.5~16.3 mm²/s, indicating a significant decrease in lubrication performance.
Verification of equipment maintenance records revealed that the diesel engine’s last lubricating oil change was in August of the previous year, using Cummins CF grade 15W/40 engine oil, with approximately 45L changed. Combined with operator interview records, it was found that the oil change was not performed correctly; the lubricating oil lines were not thoroughly cleaned during the change, and approximately 9L of residual old oil from the previous change was mixed in.
An on-site environmental inspection revealed that the warehouse storing spare lubricating oil was located in the pontoon’s hold, an area where humidity can reach up to 80% in spring. The poor sealing and moisture-proofing made the spare oil highly susceptible to moisture absorption. Comprehensive testing data and maintenance condition analysis confirmed that improperly stored old oil absorbed ambient moisture, leading to excessive moisture content in the lubricating oil and accelerated deterioration. This directly resulted in reduced kinematic viscosity and insufficient lubrication of the friction pairs, ultimately causing abnormal dry friction on the cylinder walls. This was the core cause of the diesel engine cylinder scoring failure.
III. Troubleshooting Measures and Test Results
3.1 Diesel Engine Repair Measures
The conventional repair methods for diesel engine cylinder scoring failures fall into two categories: component replacement and surface repair. For failures with deep cylinder wall scratches and severely damaged components, it is necessary to replace core damaged components such as cylinder liners, pistons, piston rings, and crankshafts. If the cylinder wall scratches are shallow and the main body of the components is intact, fine grinding can be used to complete the repair work.
After disassembling the diesel engine in this case, a comprehensive inspection and scratch depth measurement were carried out on the pistons, piston rings, and cylinder liner inner walls of each cylinder. Specific test data are shown in Table 2. The test results show that the pistons of all six cylinders of the engine have no structural damage such as cracking, deformation, or breakage. The cylinder liners do not show serious defects such as metal peeling or chrome plating loss. The overall main structure of the components is intact, and the degree of damage is relatively minor.
Table 2 Scratch depth of each cylinder of diesel engine | ||||||
| Cylinder Block | Cylinder 1# | Cylinder 2# | Cylinder 3# | Cylinder 4# | Cylinder 5# | Cylinder 6# |
| Maximum Depth | 0.21 mm | 0.16 mm | 0.08 mm | 0.06 mm | 0.06 mm | 0.05 mm |
Cylinder and Piston Ring Repair: Inspection showed that the scratch depth of cylinder walls in cylinders 1 and 2 exceeded 0.1 mm, indicating significant damage. Therefore, the cylinder liners and piston rings of these two cylinders were replaced as a whole. The scratch depth of cylinder walls in cylinders 3 to 6 was less than 0.1 mm, indicating minor damage, and no parts replacement was required. After disassembling the pistons, the inner walls of the cylinder liners of each cylinder were finely ground to eliminate surface scoring marks and restore the smoothness and fit accuracy of the cylinder inner walls.
3.2 Lubrication System Rectification Measures
The root cause of this failure was the deterioration of the lubricating oil due to moisture, resulting in decreased lubrication performance. Therefore, a thorough cleaning and oil change of the lubrication system was necessary. Specific measures were as follows:
First, the oil pan was disassembled, soaked in a special cleaning agent for 10 minutes, and then high-pressure flushed to thoroughly remove any residual deteriorated sludge and impurities.
Second, most of the old lubricating oil in the system was drained, leaving approximately 10% as the bottom oil, and then new, dedicated engine oil of the same brand was injected.
Third, the diesel engine was started and run unloaded for 20 minutes to flush away any remaining old oil in the pipeline using the new oil circulation, followed by a complete draining.
Fourth, after adding qualified new lubricating oil, the diesel engine was gradually increased to its rated speed and run continuously for 30 minutes to check the overall machine and lubrication system operation status, ensuring there were no abnormalities or potential problems.
3.3 Machine Test Verification Results
After completing the component repairs and lubrication system rectification, the diesel engine was restarted. The equipment operated smoothly without abnormal noises, vibrations, or other abnormal malfunctions. The machine break-in test was completed strictly according to the equipment maintenance manual, with a cumulative running time exceeding 100 hours, and the operating conditions remained stable throughout. During the period, the performance indicators of the lubricating oil were regularly sampled and tested. The test results all met the standards, proving that the rectification measures for this fault were effective and the equipment has been restored to normal working condition.
IV. Conclusion
As an indispensable core auxiliary system of marine diesel engines, the lubrication system not only reduces friction and wear of moving components, but also undertakes multiple functions including cooling, sealing, cleaning, vibration reduction and anti-corrosion protection, which is crucial to the long-term stable and safe operation of main engines.
Therefore, regular inspection of lubrication systems and strict quality control of lubricating oil storage and application are essential links in marine diesel engine maintenance management.
Based on the troubleshooting and rectification experience of this fault, marine maintenance work should further standardize lubricating oil storage environments and replacement procedures, prohibit the mixing of new and old oil, and establish a regular oil quality monitoring mechanism to predict and prevent oil deterioration risks in advance. In addition, timely shutdown intervention effectively prevented fault expansion, which fully reflects the significant value of real-time diesel engine condition monitoring. During vessel navigation, dynamic monitoring of main engine operating parameters should be maintained to identify equipment abnormalities and eliminate hidden faults at the earliest stage, preventing minor defects from evolving into major safety accidents and ensuring overall maritime navigation safety.
