The classic Detroit Diesel two-stroke families — 71 and 92 series — powered a great many workboats, trawlers and older motor cruisers, and a number remain in service in Australia.
Genuinely different engines
These are two-stroke diesels, and they do not behave like the four-strokes most owners are used to. Operating characteristics, oil consumption expectations, exhaust behaviour and the maintenance regime all differ, and advice written for a modern four-stroke can be actively wrong when applied to one of these.
If you are taking on a boat with one, find someone who genuinely knows the family. Their knowledge base is specialised, ageing, and worth a great deal.
Assessing one
Age is the dominant factor. Every system around the engine is likely to be as old as the engine, and parts support depends on the specific variant and on the specialist network rather than on general marine channels. Emissions and fuel-consumption expectations also differ substantially from modern engines, which matters for both running cost and for any future compliance question.
Before you buy or repower
- Which exact family and variant, and who locally works on it?
- Parts availability for that variant, through which channels?
- Condition of everything around the engine, which is likely of similar age?
- Realistic fuel consumption for how you intend to use the boat.