MAN engine life in 48 ocean

If taken care of 5-6000 hours generally, sometimes more sometimes less.

I assume you mean before a major overhaul- not before they need to be pulled out and replaced. Of course this hour figure depends on how they are treated and run to a degree. Individual engines could last much longer or shorter. I know some boat captains who have had great experiences with them and some not so great- not much different than other makes.

i am currently looking at purchasing a 1995 ocean with 800 hp man engines they have 1200 hours on them and were professionally maintained the boat was fished 50 % and the rest was cruise what is the average expectancy before overhaul i know there are many variables just wondering and what would the cost be

Yes, generally 5-6000 hours before overhauled is generally what most people see. I have an owner with 6000 hours on his 820's and they still run great and show no issues of failure, but he did just do a top end rebuild (cylinder heads) just because of the hours, turbo's etc. The bores all looked great.

Ummmm, the same exact answer that you got in your other thread asking the same exact question.

Are they much more than a detroit to overhaul

Yes, probably 25% more, but don't leak oil like the detroits, are more fuel efficient. etc. Honestly the chances on you putting 4000+ hours on that boat are slim to none. Most owners put 100-150 hours a year. That's what 25-40 years of normal usage?

Yes thank you for your help I am familiar with detroit cats and cummins never touched or owned a man new to yacht forums so look forward to talking with you again.

I think most of the motors will go 5-10K hrs but it's wildly dependent on care and usage. I've seen C-32 cats with catastrophic failures and MAN's go pfft too.
I don't know if the older MAN's have the hour logs but if they do you can get a pretty good view to usage. How much time in an RPM band. I'd probably just get a very good survey including bore scoping everything. The tech will give you and idea then of how much life is left. Lot's of 800's out there so you should be able to get someone that knows what they are doing with an assessment.
Good luck with your search.