Volvo Penta diesel (D3/D4/D6, saildrive)
Modern common-rail Volvo diesels are durable and economical, routinely good for 5,000+ hours. The cost center is the saildrive (on sailboats): a diaphragm service every ~7 years and corrosion vigilance. Parts and dealer labor are expensive.
Service and what to check
Saildrive diaphragm on the 7-year schedule; check for corrosion and gear-oil water intrusion. Diesels tolerate hours far better than gas — judge by service history, not hour count alone.
Watch usage: above roughly 250 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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