And second question is when is over-haul required on engines, other than when it has become obvious? Like age or hours.Or just run them until things start to take a turn in the wrong direction?....Thanks
Marine diesels, at least in recreational service, don't have TBOs (Time Between Overhaul) requirements like you get on aircraft engines and the like. They do have manufacturer's recommended service intervals which should be followed. And engine makes and models that have been around for a long time will have built up a reputation for having a service life of some average number of hours.
For example, the venerable Ford Lehman 120, an engine based on the Ford of England Dorset truck/industrial/agricultural engine designed in the 1950s and marinized in the 60s by Lehman in New Jersey, is said to have a service life in recreational boat applications of 12,000 to 14,000 hours before the core of the engine will need an overhaul. This is assuming the engine is operated per the manufacturer/Lehman recommendations and is serviced and maintained properly. Other types of engines may have average service lives of less hours.
It is said that the modern, high-speed, turboed diesels used in many newer boats today have average service lives considerably shorter than the old thumpers like Lehmans, Perkins, etc. Whether this is actually true or not is something I don't know. My only marine diesel experience has been with the FL120. Boating is notorious for blowing things out of proportion, so the "high speed, hot turbo engines have short lives" thing may be more myth than reality. But you would want input from a professional engine/propulsion system person like Rick B on this forum or an experienced diesel shop before you made any judgments on this issue.
There's no telling when water pumps, fuel pumps, injectors, injection pumps, starters, hoses, heat exchangers, etc. might begin to falter or fail outright. These issues will need to be dealt with when they come up. Some can be anticipated, which is why most operators change out wear items like flexible pump impellers, drive belts, zincs, etc. on a regular schedule. Other items, particularly hoses, can be monitored for potential deterioration. But some things--- like a fuel injector pipe that suddenly develops a crack or pinhole--- can't be anticipated.
When shopping for a boat the way the engine(s) were treated by previous owners is far more important than the total number of hours on the engine(s). For example, given the choice between a Ford Lehman 120 with 3,000 hours on it but with a questionable or poor previous owner record and a Ford Lehman 120 with 7000 hours on it that was operated, serviced, and maintained properly by a conscientious owner, I would take the boat with the 7000 hour engine, all else being equal.
) but the majority are only in the 2500-3600 range, the highest stated being 4400 hours. Either the old boats never got used that much, or owners are turning back the clock. If there is a 7,000 hour boat out there, it isn't for sale. BTW ... I have ~4400 on my MT34.
