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,

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.

If you are considering a boat with DD's you might find this interesting.

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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.

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.

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.

David

Comodave said:

Leaked oil..

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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. :lol:

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.

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.

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.

The generators on my tug are 6-71s. Run 24/7, 365. They have some downsides, but dependability would not be one.

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.

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.

kapnd said:

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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That is funny. Ha...Ha...Ha

Lepke, what type of craft were you on in Vietnam that had Detroits?

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.

I’ve two in my trawler 6-71’s and one in my push Boat 6-53 Maybe? I spend a fair amount of time chasing oil leaks but don’t 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

I had a pair of 6-71's in my LCM 6. Best running engines I've ever had.

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.

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.

Thanks for all the help and guidance. With the information you all have shared I can at last make a well informed choice on whether or not to buy a boat with Dad's. Just want to know what I'm getting into with whatever engines a boat has.

ScottH said:

Thanks for all the help and guidance. With the information you all have shared I can at last make a well informed choice on whether or not to buy a boat with Dad's. Just want to know what I'm getting into with whatever engines a boat has.

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Not so quick, you just asked from the owner's of DDs. Long before emission regs came out the heavy, fuel loving, oil burning DDs stopped going into boats and other applications.

My Dream Boat would have a pair of DD with the std Navy gearbox to operate a single protected center line shaft.

I have seen these in Boats and Harbors with a US Navy rebuild for $6,000 for the package.

I would remove one 6-71 and swop it or purchase a 3-71.

Inshore with fuel easily available , the 6 would push or the 6+the 3 if I really wanted to defuel rapidly.

The 3- 71 would be the cross ocean unit with the lowest fuel burn at displacement speeds .

20-30HP per 71 cylinder is normal , and good for many thousands of hours ,

30-70 hp would push any boat I could afford around the world.

As there is so much in common, either engine could be used for spare parts.

sunchaser said:

Not so quick, you just asked from the owner's of DDs. Long before emission regs came out the heavy, fuel loving, oil burning DDs stopped going into boats and other applications.

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Seems that much of the DD love here is based on sentiment rather than sensibility.
It’s hard to turn away from something that has been such a large part of boating all these years, but emissions, fuel burn, noise and of course tier 3 regs say no to the venerable DDs.
With all the great engines available today, I would not spend good money to step back in time.
I worked on a charter boat with DDs that required oil about every three hours, and the motors had to be stopped to add it. If the oil filler was opened while running, it would spew it clear to the cabin ceiling! The bilgewater would have been perfectly acceptable to pour back into the sump, but the motors just kept on going.
One of the BIG pluses of an ER that used to have DDs in it is all the space!

kapnd said:

Seems that much of the DD love here is based on sentiment rather than sensibility.
It’s hard to turn away from something that has been such a large part of boating all these years, but emissions, fuel burn, noise and of course tier 3 regs say no to the venerable DDs.
With all the great engines available today, I would not spend good money to step back in time.

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I doubt many here would strongly advocate for an older 2-stroke DD in a new build boat. Except for maybe FF.

But I think the point many have made is just that a good boat that happens to be powered with 2-stroke DDs doesn't need to be dismissed from consideration just because of the "era" of the engines.

-Chris

Last spring I did a mechanical survey on an old Chriscraft with 8V71N's. Built in 1967. Engines never overhauled and checked out perfect. A touch of cold start smoke then clean. No smoke under way. Various owners could not help themselves from "improving" electical and other systems, so engine room was a hash. But engines were just fine. Amazing.

Fifty years of service. Ready for more.

Helen Marie said:

I had a pair of 6-71's in my LCM 6. Best running engines I've ever had.

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Yep.

djmarchand said:

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.

David

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You are correct. I was talking about cylinder kits and you stated my point much better than I with regards to the impact to running them hard versus moderately at more reasonable speeds. Sorry for the brevity and confusion!

As stated, more data and opinions on boatdiesel.com and even over at yachtforums too.

In addition to boatdiesel.com, which is excellent, the Hatteras Owners Forum has a ton of good threads by knowledgeable owners, as virtually all vintage Hatts were DD powered til the 2 strokes went out of production. I loved my 8v92 tti's.

Fletcher500 said:

Lepke, what type of craft were you on in Vietnam that had Detroits?

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The USN up to that time was a heavy user of DDs, especially the 71s. Many ships from WWII had DD emergency generators. I ran PBR - 2 6v53 running jets, Mike boat - 2 671s, ASPB - 2 12v71s, also generators w/671, 471 8v71, 12v71. Swift 2-12v71s, too. And another late war jet (can't remember designation -flat bottom, small bow ramp, carried about 30 troops @ 35kts) - 2 8v71s. Also YTM w/2 671 generators.
At the time I was told the 53 series was just military and was surprised to run into various 53 models later. I learned how to overhaul DDs in VN while passing the slow times. I've run many other engine types. Cats and Cummings are great engines but I guess I like DDs because I know them so well, hate injector pumps, never had a DD failure even with damage. PBR jets had a removable top and a hose for water removable. You could have a hell of a hole and still float if the jets were running.

In my current boat I can have a normal conversation in my "living room/bar" directly over 2 671s @ 1800 rpm. Proper sound proofing makes all the difference.