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Old 12-04-2017, 11:33 AM   #1
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Detroit Diesels

Hi Everyone,

Still trawler shopping. If your boat has Detroit engines, I'd live to hear your thoughts about fuel economy, maintenance, longevity, etc.

Thanks,
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Old 12-04-2017, 11:50 AM   #2
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I had the 8V71 in a 46 ft boat and loved it. They are not the quietest or most fuel efficient but spare parts and mechanics are plentiful.

They run forever but should you need a rebuild, most can be done in-frame. I really enjoyed mine.
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Old 12-04-2017, 12:06 PM   #3
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If you are considering a boat with DD's you might find this interesting.

https://www.dropbox.com/s/imjxb9s8yl...pecs.docx?dl=0
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Old 12-04-2017, 02:27 PM   #4
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Depending on the model and specs, you will get a lot of differing opinions. Starting with a lot of love for the older 71 series which has origins in the 1930's. Treat them right and they last forever. They can be loud (I love the sound personally) and a lot of people say they go through a lot of oil.

Do research on the CID/HP ratios since they can be overcranked a bit and if they are run to hard there's lots of people that say that will pull in the service intervals significantly (as short as 500-1000 hours). Many recommend keeping that ratio below 1.0 or run them at lower RPMs/load factors etc to keep the service intervals closer to 3000 hrs.

I have 6v92's at 625 HP. I did some recent trials and got these numbers:
@ 1200 rpm = 10.8 knots SOG @ 6 GPH ea.
@ 1500 rpm = 12.2 knots SOG @ 11 GPH ea.
@ 1800 rpm = 15.0 knots SOG @ 19 GPH ea.
@ 2000 rpm = 16.6 knots SOG @ 23 GPH ea.
@ 2150 rpm = 18.7 knots SOG @ 29 GPH ea.
@ 2300 rpm = 20.5 knots SOG @ 35 GPH ea.

Lots of really good DD stuff over at boatdiesel.com as well.
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Old 12-04-2017, 03:10 PM   #5
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I had twin 6V53s in a previous boat. Ran like tops. Leaked oil. Burned about 1 gallon every 24 hours or so underway. Never had any breakdowns or really any problems with them. They misted oil from the air boxes, had a mechanic that made a Rube Goldberg collector that worked great to collect the oil mist so the engine room became clean after lots of scrubbing. Overall not bad engines, just have to keep a lot of oil diapers on board and carry extra oil.
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Old 12-04-2017, 04:02 PM   #6
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Tozz above presents a dismal view of service intervals (I suspect he means doing cylinder kit overhauls) for the DDs. I suspect he is referring to sport fishermen who can go through cylinder kits every 1,000 hours if they run them near the pins.

If you run them moderately, they will go lots of hours, probably more than 10,000 hours before requiring a kit overhaul. Any trawler run at displacement speed with one or more DDs will certainly be moderate use.

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Old 12-04-2017, 04:08 PM   #7
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Quote:
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Leaked oil..
I took a picture of my 6-71 and hung it on the wall. The next morning there was a puddle of oil under the picture.
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Old 12-04-2017, 04:08 PM   #8
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We had a old 6v71 in a house boat we owned. They were both great motors. Only problem I can really remember was having to replace the shut down on the 671 a few times. Oh and the fact they are like a tom cats they mark their territory, with oil instead of piss.
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Old 12-04-2017, 04:55 PM   #9
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I wouldn't shy away too much if the boats you were interested in had NA Detroits. I had a 6V53 NA in my last boat , a 44' Chesapeake deadrise, and it didn't leak a drop. Noisy as hell but no leaks. The newer Detroits were MUCH better. My good friend had a pair of 16V92's in his sportfish. They were probably way over injected & everything else @ 1450HP each but they never leaked a drop either & we ran it hard to South Florida & back every year for about 8 years.
I was looking at Hatteras LRC's on Yachtworld last night, as a matter of fact (just planting seeds in my wife's head right now ). They all had 53 & 71 series DD naturals in them. Fine workhorses.
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Old 12-04-2017, 05:16 PM   #10
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I've been running 71 series engines since I was a boy and am 69 now. I ran them in Vietnam, on commercial boats, yachts and as auxiliary engines on tugs and ships. I've done my own overhauls since 1969. The sleeves are marked and an engine can be rebuilt exactly as they came from the factory. You don't need rocket science.
I love 'em. I consider them to be one of the most reliable engines for marine service ever built. Because they're 2 cycle, you get a power stroke every revolution. They have no injector pump to fail and require no electricity beyond starting. And with hydraulic starting can be started manually. They will run until fuel is exhausted. They get you home. In the military I have run them, out of necessity, in extremely damaged condition, yet they still delivered enough power.
Much of the oil leaking issue comes from the original design 671s using old style seals. Newer engines don't have to leak. They do burn some oil. Probably from the intake sleeve ports at the bottom of the piston movement. I don't consider it excessive.
Parts are available anywhere in the world, even Russia. Many manufacturers make replacement parts besides Detroit. The 671 as designed was able to be rebuilt in primitive conditions including all their accessories, blower, injectors, pumps and so on. I bought my current boat largely because of the 671s. I cruise a 83', 80 boat at 10 knots using about 8.5 gallons an hour. Economic speed is somewhere around 7 knots using about 4 gallons an hour. High speed boats using Detroits do burn a lot of fuel, but so do other engines using similar amounts of hp. Newer electronic controlled engines burn cleaner and use less fuel, but in a lifetime on the water, I have learned everything electric or electronic fails. Usually without warning. People I know running commercial boats with newer engines carry hundred of dollars or more in electronic spares.
As I've said many times, The EPA can take my Detroits when they take the starter buttons from my cold dead hands.
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Old 12-04-2017, 06:44 PM   #11
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The generators on my tug are 6-71s. Run 24/7, 365. They have some downsides, but dependability would not be one.
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Old 12-04-2017, 06:48 PM   #12
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Going back to a DD after all these years would be like getting back together with my ex-wife. I left her for good reason, no need to go back there ever again.
She smoked, bled, leaked, and fumed constantly, refused to work hard without some major breakdown, and the cost of maintaining her was not worth the rewards.
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Old 12-04-2017, 07:14 PM   #13
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I had 8v71na Detroits. They are as long-lived and rugged as any modern diesel. Mine didn't smoke and got good fuel economy at displacement speeds. Good parts availability and cost. The cons? Mine leaked oil like a sieve and the mechanical engine noise was deafening, mostly the injectors. I like the exhaust note....sounds something like a turbine. I have Cummins now, but I have some nostalgia for 2-cycle Detroits.
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Old 12-04-2017, 07:15 PM   #14
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Quote:
Originally Posted by kapnd View Post
Going back to a DD after all these years would be like getting back together with my ex-wife. I left her for good reason, no need to go back there ever again.
She smoked, bled, leaked, and fumed constantly, refused to work hard without some major breakdown, and the cost of maintaining her was not worth the rewards.
That is funny. Ha...Ha...Ha
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Old 12-04-2017, 07:46 PM   #15
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Lepke, what type of craft were you on in Vietnam that had Detroits?
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Old 12-04-2017, 08:09 PM   #16
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I have nothing bad to say about old DD engines. Would not be my first choice in a trawler application but if I was running a Sport Fish, a pair of DD 1271 or 892's would be my first choice. Then again I have seen some 6kt boats out ther running 453's that have been around sice WWII. I would never walk from a boat because it had DD.
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Old 12-04-2017, 08:27 PM   #17
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Iíve two in my trawler 6-71ís and one in my push Boat 6-53 Maybe? I spend a fair amount of time chasing oil leaks but donít seem to have any major issues besides an in-frame a year or so ago, had water in the oil, all three run like tops
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Old 12-05-2017, 12:58 AM   #18
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I had a pair of 6-71's in my LCM 6. Best running engines I've ever had.
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Old 12-05-2017, 04:02 AM   #19
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I've got a pair of Screaming Jimmies 8v71n's in my CL66.
They have never failed to start instantly, leak a manageable amount of oil, probably burn a bit as well. Fuel consumption quite good provided I keep below 9 knot cruise, we top out at 13 knots.
Parts are easily obtained and are so cheap I laugh (I had Volvo's once.)
I keep my oil level at the half way mark on the stick, lowers the oil loss quite a bit.
Engine room noise is probably the biggest issue, earmuffs all round when in the ER. On the bridge it's fine.
Not a modern engine, and thats fine by me.
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Old 12-05-2017, 07:55 AM   #20
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I have posted many times about having DD's. I have 6-71TIB's. At 1100rpms and 8knots I burn 7 gph total.with a 15kw genny runny at about 30% load. At 1800 rpms I'm running 14 kts and burn 18 gph with genny. At 2000 rpms I'm running 20 kts. I don't have a fuel burn as I only do that for about 15-20 minutes a trip after 5 or 6 hours running. Not bad for a 50k aft cabin motoryacht. As far as taking care of them. Change the oil every 250hours and change the coolant every 2 years with Powercool and don't overheat them. Other than that they will be running 50 years after we are long dead.
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