Welcome jibs up!
It is the nature of this place that when you ask a question you often get 50 questions in response and few answers.
Engines generally fail or wear out. Accessories (attached to engines) usually fail.
Wear out - the oil
and bearings are designed to keep the parts
in the engine
separated and reduce the amount of wear. Wear still happens all throughout the engine. Eventually wear causes all sorts of signals to appear. Oil consumption
increases, smoke can increase at times, temperatures shift, compression
reduces. clearances increase. The engine relies on compression to run. Compression demands a well sealed cylinder. The cylinder needs openings to allow fuel
in, to allow exhaust
out (valve and valve train system) and to allow the gas to compress and expand (the piston and cylinder itself).
Wear out is slow and predictable.
Failure - Sometimes the parts are stressed due to lack of lube, overheating
, or sometimes just bad assembly. In this case parts can work loose. You may have a sign in advance such as a loud tapping, or knocking or engine shaking. These are very bad signs and must be investigated immediately.
How to tell? - If the engine starts easily, runs well and seems to produce good power then the engine is probably ok. Marine
(yacht) diesels get very little use and will last a very long time. They handle abuse well and so it is very strange to hear someone say, "It is about to fail in 20 hours."
I would ask, "What specifically is about to fail?" I don't doubt he is a decent mechanic
but if you are new to the boat and he has been maintaining it 2 years he might have some insight. I would question him more. As to his motive of money
- he advised you to find someone (else?) to rebuild
the engine. If he is not making anything on the deal he might be sincere.
It bears questioning hiim more about his opinion. Why will it fail? What will fail? How has this condition changed over the last 2 years?
What is the oil consumption
? What is normal?
What are the temps (oil and water) trending? How has this changed?
What is the compression in each cylinder? How has this changed?
What are the valve train clearances? How have they changed?
Finally - How do you use the boat? Daysailing? How do you use the engine? Into slip, out of slip? Motor
saiing 8 hours per day? Full time? Weekends year round? Weekends summer only?
If the usage of the engine is low and you could tolerate a tow someday and there are no grinding, tapping, slamming, pounding, knocking noises, I would keep on driving. You amy get 2-3 more years out of it.