Looking at a 1990 45C, Suggested details to look into?

Me personally I would wait till a 95 or so with MANs comes on the market. Nothing against Detroits but you know you are going to need expert help with those at some point and as Ralph said the experts are aging out. I am hearing that you have to be careful buying parts as some of them are of marginal quality. Keeping a boat reliable is enough trouble without having to worry about finding good parts and competent techs.

You still have to shop for a quality MAN shop. Still a few MAN slobs out there
But they are quieter, cleaner and more power per cubic foot of engine room space.

MAN designs are just 50 plus years newer in a 95 built boat.

While I'm typing away, I'll bring up Cat power.
Stay away from anything smaller than 3406s.
Quickly keep walking (run) past anything with 31XX or 32XX model numbers.
Yes, I'll take some heat on this post.
The stuff I take from / for my friends.

I'm shocked to hear you have a 1990 boat with non-DDEC. My 1994 boat was DDEC II. Here's what I found for DDEC info:

The first system, DDEC I, lasted from 1987 to 1992, when it was replaced by DDEC II. All Old Style Series 60 11L & 12.7L engines were controlled by DDEC I, II or III until 1998.

My 1993's are mechanical.

Benefits of the DDEC?

It offeres computer controlled tuning to other wise very dumb mechanical injectors.
Over fueling issues went away.

Max HP per lung is achieved.

Electronic engine controls. No more push -pull cables.
This also offered a better sync solution between the engines.

Mostly Propitiatory, but a digital data buss offering better engine monitoring displays.
Early digital dash.

IMO; the engine idles smother. Idle recovers quicker when clutching around the dock.
IMO; the engine sounds better. A cleaner-sharper bite in the exhaust bark.
IMO; stinks better.


Downsides of the DDEC?

Hard for the DIYr to fix by him(her) self.

Expensive parts. Only one repair shop.

Max HP per lung is achieved.

Sometimes, when it fails, that engine is down for a day, or two, or three, or,,,

Your just could be a 71 series, not really in this discussion.
If your 92s liners and O rings have never been touched in 40 + years, Then somebody is fibbing somewhere or divine blessings may have to be brought up.

Easy now Ralph. My 92's have about 2400 hours and haven't been apart since they were manufactured in 92 for a 93 Post 46.

Witch is very different from the 80s.
And yes my friend. I may have gotten carried aweigh,
But I caution even your sweet and luved engines, those liner O rings are not going to last for ever.

Yep, I say every spring, " this is the year for pistons and liners". Maybe next year.