Marine diesel inboard (Yanmar / Cummins / Universal)
Conventional shaft-drive marine diesels (Yanmar and Cummins especially) are the most durable propulsion in pleasure boating — 5,000–10,000 hours is normal with maintenance. On sailboats, a repowered modern diesel replacing a legacy gas Atomic 4 adds significant value.
Service and what to check
Judge on oil analysis, coolant condition, and service records over raw hours. Check the heat exchanger, mixing elbow (on the exhaust), and motor mounts.
Watch usage: above roughly 300 hours/year, this family starts losing reliability points — always weigh total hours against the boat's age, and on any outboard or I/O over a few years old, insist on a compression or leak-down test before money moves.
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