To get really good info on the DD's there is a forum http://boatdiesel.com/. You definitely do not want to overheat a DD but as long as you keep good maintenance on them, clean fuel, filters, oil, etc. they are work horses. If you don't over prop them, run them hard, and their not too high of HP you should be able to get several thousand hours on them.
Interesting...several thousand hours of use...as in 2000 hours before overhaul? I have been told 692's are time bombs so I am a little hesitant...I believe these in particular are 550 hp each....good information to digest!
I think that most of the "Time Bomb" issues were with the 635hp DDEC's. If propped correctly (not over or under and should be 2300 - 2350 rpm at WOT), maintained properly (oil, fuel, heat exchangers, filters, zincs, etc.) , and not ran hard all the time it should not be a problem to get 2000 hours.
She looks like a fine Vessel. I agree get a Detroit Diesel Mechanic involved and best of luck to you. Happy Sailing.
David Hi, What size inverter would run all of that load and what are you running for batteries? Where did you install the water maker?
I would count on a full rebuild of that engine (that needs a top overhaul). So, that's around $18k plus count on $5k-$10k for all that goes into getting the engine out and then back in and additional things that are found during the process. Overall, it's a really great idea to find a boat that is already running perfectly and has the upgrades you want.