life of a 671tIb


New member
I found the perfect 62 4 state room boat but I am worried about the engine hrs. I sold my 100 slip marina in Michigan off lake Michigan and are ready to somewhat retire. The boat has 671TIB Detroits in it with very close to 5000 hrs. My budget is around 250k and the boat is 280k. I can handle the 30k extra but will be hurting if I need a complete rebuild on the engines. I plan on living aboard her in the summers around the Detroit area and do high end charters to Cedar Point, Put-In-Bay and Niagara Falls. My question is can I get another 1000 hrs out of them before a rebuild or am I playing Russian roulette. At close to 10K per 5 day charter I only need 1000 more hrs for the rebuilds. Also any estimates on the rebuilds would be nice. I dont know if the engines can be pulled easily but it is a stand up engine room with a lot of space for a in frame.


Silver Medal Contributor
Inlines or V-6's?...just curious really.

Going out on the water in a boat is a crapshoot even with new engine's. NEW stands for
Never Ever Worked.

I can't answer your questions but I will say that success or failure for your plan likely will reside in the quality of care the engine's have received thus far.

If the vessel comes with carefully detailed log books that include maintenance entries that would be a very encouraging sign.

You might want to think of the boat as a highway truck or bus for determining the probability of making your goal.

What I mean is that a rough formula for converting engine hours to miles on an odometer is times 60.
60 X 5,000 = 300,000 miles.

The 71 series Detroit engine can easily reach the 500,000 highway miles in trucks and many have surpassed 1,000,000 miles before overhaul.

Having said that, you have to consider that marine duty is typically much more stressful on engines as it's often said a displacement hulled boat is pretty much always pushing "uphill". So, I would shave off a bit of longevity due to that.

Shave off a little more for the turbos being used to sqeeze out additional horsepower. Although, bypass blowers helps alot with that.
The turbos don't always make the full trip that the base engine will as they are hard working but delicate.

The same goes for injectors. Especially if the fuel isn't of high quality and kept meticulously clean and water free.

But, with good history and perhaps some pre-purchase inspection to include passing oil sample tests, I would say that you're well within the window of making it.

The 71 is a very tough, reliable engine that is famously made to run all day, night and week at maximum governed speed if properly fed and cared for.

Whatever you choose I wish you fair weather and good fortune.


Regular Contributor
High horsepower 671 Detroits usually go 3-5000 hours between overhauls. It depends on the maintenance and the guy driving them. I have got as much as 11,000 hours and always 7,000+. But I watch the exhaust gas temperatures and keep my oil clean. Party boats with hot dog drivers get as low as 1000 hours. High exhaust temps break down the internal cylinder parts. Most people run full throttle and use them up fast. I rarely run above 80% of hp and have clean oil.
If the engines start easy, there's no smoke after they're warm, and no oil in the exhaust they probably have 1000+ hours left. They can be rebuilt in place, I've done it many times. An engine kit (post Biden) is about $2000+ now. I've always used after market parts and been happy with the results. From Detroit 2 or 3x more. Having the head rebuilt was about $1200 (pre Biden). Haven't priced it lately. Most people replace the oil pump, rebuild the turbo and the coolant pump. Things you don't replace need to be inspected. If you're not a mechanic and pay to have it all done, they supply parts, about $30,000 an engine (pre Biden).


Silver Medal Contributor
make sure you get an accredited marine surveyor to look it over before you commit...and have them find you a good engine surveyor...between the two of them, you will get a much better assessment on the current condition of all of the major systems involved...if they find anything, you can adjust the price in your offer accordingly...