<![CDATA[Marine main diesel engine failures remain one of the largest sources of operational risk and commercial loss in merchant shipping, with loss of propulsion consistently ranked as a top machinery casualty category and engine maintenance quality now an explicit criterion in commercial vetting regimes such as SIRE 2.0. However, existing reviews largely treat maintenance strategy selection as a generic engineering problem, without systematically linking specific failure-mode behavior to strategy assignment or consolidating condition monitoring techniques into a subsystem-specific, actionable guide; this leaves fleet operators without a unified decision tool connecting failure diagnosis, strategy selection, and monitoring technology. This review therefore aims to (1) identify the dominant failure modes and root causes of marine main diesel engines reported in the peer-reviewed literature, (2) systematize available maintenance strategies through an integrated Failure Mode and Effects Analysis-Reliability-Centered Maintenance (FMEA–RCM) decision framework that assigns each strategy to specific subsystems; and (3) map condition monitoring techniques onto main engine components to support the transition from time-based to condition-based maintenance (CBM). A narrative literature review methodology was employed, combining structured database searches (Scopus, Web of Science, Google Scholar) with backward citation tracking across 31 peer-reviewed journal articles, textbooks, international standards, and maritime authority casualty reports published between 1997 and 2025, synthesized thematically using the bathtub failure-rate model and FMEA–RCM decision logic as the integrating analytical framework. The review found that the fuel injection system, cylinder components, turbochargers, and the lubricating and cooling oil systems are the dominant contributors to main engine unreliability, with root causes concentrated in fuel and lubricant quality, thermal overload, and deferred maintenance rather than in inherent design deficiency. A hybrid maintenance architecture combining time-based tasks for age-related failure modes with CBM for randomly occurring, detectable degradation emerged as the most effective strategy, with lubricating oil analysis, thermodynamic performance monitoring, vibration analysis, and thermography constituting the principal CBM toolkit, and organizational integration into the planned maintenance system identified as the key remaining implementation barrier..]]>
