12V71TI service/experience

[nor'easter]

As my last few threads have stated, I am gathering info for a possible new to me Hatt in the future (after my current 39SX sells).
I am thinking of moving up to a larger C boat, and note that a number of them were fitted with 12V71s. The early 53C with Ns and later with TIs at 650hp. Given that engines displacement, I would think that the Ns or the 650 TIs would give acceptable service life if maintained properly. I have learned (mainly from here and bd.com) that the 735 and 800+ 12V71s are 1500-2000 hr plants, but have seen a number of Hatts with the Ns or 650 TIs in brokerage listings with 3000+ hrs and still "strong". Thoughts from the book of genesis or the grand poohbah?

[StratPlan61]

I have the small 'TI version' 12V71s (650hp). I like them and they run great. They have about 2400hrs on them and they smoke a little on start-up. I just added a set of Wolverine oil pre-heaters which eliminates 95% of any cold-start smoke. Admittedly I loaf them, partly to save fuel and partly to spare them any real stresses.
I have heard all of the stories: if you loaf them, you'll wreck them; you must run them at WOT at least 20 minutes everyday; etc. It's like asking somebody which viscosity oil to run in them - everybody has the 'right answer' according to them???
I think the SF had the bigger versions w700+ and 800+ HP ratings. People tell me these versions are tweaked up too high and don't last as long, who knows??
I baby mine and they work great. The engine surveyor said they could use rebuilds in the next few years - we'll see how they do. After running a 10-12hr continuous day, each motor takes 1-2 quarts of oil, not too bad considering the 13.5 gal oil capacity. Who knows, maybe I'll just feed 'em oil for awhile and keep talking to them? Good luck with your sale and potential purchase.

Bear'
1984 61 MY Strategic Plan

[luckydave215]

I have the 900 hp version and at 1900 hours the (very thorough) engine survey gave them a clean bill of health, expected another 4000 hours if treated the same as they have been. The previous owner (and I) usually run them at 1200 rpm, little more than displacement speed, with 20 minutes at 1800 every 5 hours or so.
If you run the piss out of them, expect expensive rebuilds at 2000 or less hours.
My friend is the captian of a long range charter boat that got over 100,000 ours out of a set by running them gently.
That's not a typo.

[Genesis]

The naturals, taken care of, will probably outlast YOU.

The turbo engines are another matter. As you approach 1hp/cid displacement, service life suffers badly if you actually use the power you have available.

This is true for all diesels.

As with any Detroit, the keys to long life are clean oil and never overheat them.

12s are lots of fun to run the rack on, but its not hard - just tedious.

[nor'easter]

Thanks.
I figured that the general rule of thumb regarding hp/cid applied here as well. I am also interested in knowing if these engines were notorious for anything in particular rearding their design or performance, as well as things to watch out for.
I couldn't see much on boatdiesel.com. There are pages and pages of 71 series posts, but mainly about the venerable 671 and then the 871.
Thanks again.
NE'r

[Boss Lady]

aren't the 12v71 are really just two 6v71s tied together or is that the 16v series that are?

[Freebird]

I recently purchased a 58TC with 12-71N's. They run fine and cruise the boat at 16-17mph @ 2100. I usually have time constraints when I cruise and would sure like to get into the 20's at cruise without abusing whatever puts me there. Can these engines be upgraded short of going with a major overhaul and adding turbo's? Would it make more sense to replace them with TI's to satisfy the need for speed? I had a guy tell me he would advise removing the 12-71's altogether when it came time to rebuild (referred to them as dinosaurs) and replace them with late model 6's or 8's. Anybody been there, done that?

[Genesis]

There's no inexpensive option here, and bolting turbos on those engines is a VERY bad idea - the compression ratio is different between turbo and NA engines, for one thing!

How much coin are you willing to toss on this? I'd go slow and save the fuel, to be honest - but if you must, then you're talking about a repower one way or the other.

[J's Dream]

aren't the 12v71 are really just two 6v71s tied together or is that the 16v series that are?

The 12's should be 2 6's together, the 16's are 2 8's.

[luckydave215]

My 12's are one piece blocks. I think they all are. (but I'm not sure)
It's the 12 and 1692's that are bolted together.
As far as maintainance or service issues, they are the same as any other 71 series DD's. Keep clean oil in them, DON'T overheat them, and flush out the heat exchangers every couple of years. Replace the raw water impellers and zincs annually.
BTW if assembled correctly, they hardly leak at all. Some examples none at all.