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Old 29-01-2020, 14:02   #46
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Re: Babying a diesel engine

Hopefully even the rings float on an oil film, that’s the purpose of the cross hatching of the cylinder, to hold a thin film of oil. Wear those cross hatches off or clog them with glazing and ring wear accelerates quite a bit.
Older design engines will burn a little oil even when in perfect condition, and the Brits did a study decades ago that showed when an engine began to consume a small amount of oil that the cylinder wear rate dropped quite a lot, because that slight oil burned ensured the compression rings were lubricated.
I believe Modern materials are so advanced that rings may not require as much lubrication anymore.
Way back when the Brits used to be the most advanced engine builders there were, back mid 20th Century.
It’s the camshaft and lifters that are the highest loaded portion of a typical engine, that’s steel on steel, no bearing material, bearing material wouldn’t stand up to the forces.

The old as in I guess 60’s and 70’s Mercedes Diesel engine cars had a min required oil burn, I forget what it was but my old 220 Mercedes burned I believe about a half quart every 1000 miles, and no car motor of the day lasted longer than those old Mercedes motors.
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Old 29-01-2020, 14:31   #47
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Re: Babying a diesel engine

our 40' 7.5mt cruising cat is well over engineed imho. pair of 4JH yanmars @ 55hp ea, where usual in this size would be 30-40hp

this has resulted in me usually running engines at too low rpm (1500 or so) and STUPIDLY not bumping up the revs every so often to heat the engine/s up properly.

result is one engine is blowing some white smoke ie i have (i believe) glazed the cylinders.

now being much more conscious about running at higher rpm and / or boosting rpm for short periods.

but what to do about the existing glaze ? is it true that this can only be fixed by dismantling and honing ?

cheers,
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Old 29-01-2020, 16:31   #48
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Re: Babying a diesel engine

Quote:
Originally Posted by chrisr View Post
our 40' 7.5mt cruising cat is well over engineed imho. pair of 4JH yanmars @ 55hp ea, where usual in this size would be 30-40hp

this has resulted in me usually running engines at too low rpm (1500 or so) and STUPIDLY not bumping up the revs every so often to heat the engine/s up properly.

result is one engine is blowing some white smoke ie i have (i believe) glazed the cylinders.

now being much more conscious about running at higher rpm and / or boosting rpm for short periods.

but what to do about the existing glaze ? is it true that this can only be fixed by dismantling and honing ?

cheers,
Have seen other posts where they say to try running for an hour or so flat out once engine is up to operating temp of course.

Worth a shot anyway as rebuild cost will be a lot

I'm not familiar with common rail turbos so can't speak from experience

Maybe try only using one engine normally so you can load it up more? Don't know if that works for you. Obviously docking would be problematic but for long runs?
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Old 03-02-2020, 07:42   #49
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Re: Babying a diesel engine

Did i understand this question correctly? A marine surveyor asking about proper engine treatment? Follow the manual of the manufacturer! General wisdom in mechanical engineering, there is a calculated life time of every bearing etc. Higher load - shorter live. And yes, to low a load brings unfinished burning of diesel. So run it 60 to 80%, clean it w 100% from time to time, specially after long trolling or battery charging. And make sure your drive train is set up well!
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Old 03-02-2020, 08:24   #50
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Re: Babying a diesel engine

Most wear occurs at engine startup, cold engine and time taken to create optimum oil pressure. Larger Diesel engines have oil priming pumps to ensure there is oil pressure prior to startup.
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Old 03-02-2020, 08:31   #51
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Re: Babying a diesel engine

I used to think running slower was good for my diesel engine, but have learned otherwise. Rebuilt injectors after 1,000 hours also reduced the smoke to almost nothing. The recommendation I got and now do is to at least run at 80% of max rpm for a few minutes every time the engine is used, or every hour or so. No smoke now.
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Old 03-02-2020, 08:33   #52
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Re: Babying a diesel engine

I have a 1973, 53 ft Gulfstar motor sailer that has been around the world twice.
My generator has a four cylinder Kabuta motor.
It runs constant 1800 rpm. I have seen the same motor as an onboard running 3800 rpm.
My generator has over 16,000 hours on it and does not burn oil
My Perkins 6.354 has over 20,000 hours on its third rebuilt. It burns no oil between filter changes.
It will top out at 2800 rpm but I have typically run it between 1200-1500 rpm.
I guess I baby it to keep fuel usage to about one gallon an hour when motor sailing.
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Old 03-02-2020, 08:41   #53
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Re: Babying a diesel engine

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Originally Posted by Woodland Hills View Post
I run a pair of Detroit Diesels and it is mandatory that they be run up near WOT periodically to warm them through and burn all the spot deposits off of the turbos. If I don’t they smoke a bit more on cold starts and slobber black goop (fuel and soot) that looks like oil leaks. Redlined at 2100 and I run them up to 1950 on plane around every 20 hours or so. Some say it should be more often, but this seems to work. They leave a big cloud of smoke for a few minutes and then clear. Then it’s back to 1000/1250.......
Ditto
Same for my 6-71 naturals
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Old 03-02-2020, 08:48   #54
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Re: Babying a diesel engine

I'm the 3rd owner of a '91 Grand Banks trawler. It's powered by two Cummins 250 hp 6BTA 5.9 M1 diesels. Currently have around 2000 hours each. Max rpm 2600. I usually cruise at around 1200 to 1500 rpm, +/- 10 knots, depending on sea conditions, bottom condition, etc.

Previous owner told me at the end of a day out on the water, getting close to home, he ran the engines at high rpm (22-2400) for about 20 minutes, then settled back down to low rpm through the channels and back to the dock. I took his advice/experience and have been doing the same.

The motors are in very good condition, do not use oil, and start right away. I keep them clean, change fluids annually, winterize them every year, and keep the seawater cooling system clean. I visit them often; listen to them, smell them, talk to them, thank them.

Still running the same original injectors.

I've been following his routine since I bought the boat in winter 2017-18.

All good.
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Old 03-02-2020, 08:49   #55
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Re: Babying a diesel engine

"Running near max rpm for long periods (say for 80% of its operational time) simply must increase wear simply because the engine is doing more rotations in a given time."

The couple between propellor and water isn't perfect, but it is pretty good, especially at a fixed speed. More RPMs is equivalent to more distance traveled per unit of time. The engine takes about the same number of rotations to go a given distance, no matter how many RPMs it is running.
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Old 03-02-2020, 08:58   #56
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Re: Babying a diesel engine

I'm in the 'don't baby it' camp. Chronic light loading leads to "cold" running, i.e. the exhaust and oil temperature are lower than when running more heavily loaded, which in turn does increase the accumulation of carbon on valves, rings and turbos, and sludge/varnish in the oil-lubricated portions of the engine. I often hear brokers at boat shows telling visitors this is no longer a valid concern with electronically controlled diesels, however, while electronically controlled engines are better at dealing with this issue, the cold running problem, and some of its side effects, remain problematic. Some engines, some Cummins models and MAN do include an oil thermostat, which is beneficial in preventing the oil sludge issue. Diesel gensets are notorious for suffering from cylinder glazing, particularly as a result of improper break in, when chronically lightly loaded.

Having said all this, people are going to run planing vessels at displacement speed, there's no way around it, so the best you can do is to periodically run up to higher loads, to elevate oil and exhaust temp, for 10 minutes or so, every few hours of tun time. Wide open throttle is not necessary for this practice, just a higher load, usually 50-75%. It's a good practice to ensure you engine is capable of doing this in any event, in case you need that power in an emergency.

Two articles on the subject...

https://stevedmarineconsulting.com/t...under-loading/

https://www.proboat.com/2010/09/wide-open-throttle/
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Old 03-02-2020, 10:07   #57
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Re: Babying a diesel engine

Quote:
Originally Posted by Woodland Hills View Post
I run a pair of Detroit Diesels and it is mandatory that they be run up near WOT periodically to warm them through and burn all the spot deposits off of the turbos. If I don’t they smoke a bit more on cold starts and slobber black goop (fuel and soot) that looks like oil leaks. Redlined at 2100 and I run them up to 1950 on plane around every 20 hours or so. Some say it should be more often, but this seems to work. They leave a big cloud of smoke for a few minutes and then clear. Then it’s back to 1000/1250.......

This and the previous entry pont out the importance (dixit Yanmar) to redline the engine every 3-4 hours. One very noticeable consequence is a much lower, near zero, oil consumption. This nugget was told to me recently by a retired Yanmar mechanic in Corfu. Wish I had know this for the past wasted forty years!
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Old 03-02-2020, 13:40   #58
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Re: Babying a diesel engine

I had the Yanmar 3gm30f on a 35 foot boat for about 25 years. It was a marvel by me. It survived my approach of just babying it. I found it a comfortable ride with amazing fuel economy running at 2200. There was an upgrade boat that I was investigating but the issue was a large number of new motors getting fried. Apparently the installation did not have a large enough exhaust to deal with high speed for long periods of time. I gather they don't mind high speed but everything has be right or they can go wrong. My attitude is the extra knot is not worth the noise and risk.
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Old 03-02-2020, 13:44   #59
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Re: Babying a diesel engine

While I was running a high performance motor yacht that was powered by 12 cylinder CAT's, we spend a lot of time working with the CAT specialists and were advised by them that the ideal for those engines was 80% load.

Each time they serviced the engines (250 hrs) they pulled the data from the ECU (Engine Control Unit) and recorded everything.

CAT actually has a complete cycle that is recommended and I don't remember the specifics, but it was basically 80% load with 10 minutes every hour at 95-100% load if I remember correctly.

Diesels like to run under load as it keeps them at the proper temperature and prevents coking issues which cause additional wear.... it's not uncommon to find 30 year old diesel engines in yachts still running perfectly, with perfect compression and oil analysis that shows little or no wear.....
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Old 03-02-2020, 14:56   #60
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Re: Babying a diesel engine

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Originally Posted by Herb Shallcross View Post
.........

The couple between propellor and water isn't perfect, but it is pretty good, especially at a fixed speed. More RPMs is equivalent to more distance traveled per unit of time. The engine takes about the same number of rotations to go a given distance, no matter how many RPMs it is running.
This is not even remotely true except for one special case which is motoring in a flat calm with no current and when hull speed can only achieved at the rated redline rpm.

Unfortunately this is a rare event for many of the times when the engine is in use.
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