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Old 27-01-2020, 18:37   #1
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Babying a diesel engine

As a marine surveyor I go on a lot of sea trials and I often hear owners say they do not push their Diesel engine beyond a certain rpm. I used to be in the same mindset thinking that the lower rpm will help the engine live longer?
But for years I have been observing trucks, earth moving equipment and even my Kia diesel car (320,000km). These engines all still last a long time despite being flogged fairly hard. So is it really going to make a difference to my engine life if I run my Yanmar 2GMF at 2000 or 3000 rpm?
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Old 27-01-2020, 19:09   #2
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Re: Babying a diesel engine

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Originally Posted by Fore and Aft View Post
As a marine surveyor I go on a lot of sea trials and I often hear owners say they do not push their Diesel engine beyond a certain rpm. I used to be in the same mindset thinking that the lower rpm will help the engine live longer?
But for years I have been observing trucks, earth moving equipment and even my Kia diesel car (320,000km). These engines all still last a long time despite being flogged fairly hard. So is it really going to make a difference to my engine life if I run my Yanmar 2GMF at 2000 or 3000 rpm?
Cheers
Given your 2GMF is already 37+ years old and has a rated max rpm of 3400, it probably isn't going to make much difference now!

A64pilot makes a good case for not running the engine at or near max rpm (with respect to internal wear) and I think his arguments have merit.

My take is that running them at very low revs (say 1000rpm) unloaded is bad.

Running them loaded enough to come to operating temperature is good.

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.

However at the end of the day, it seems most small boat engines simply die from lack of maintenance and very low use. An engine letting sitting for months and then run for 20 minutes is bad. Light rust forms on the cylinder walls and then gets removed at the start only to be left again for another few months. Acid in the oils sits for months at a time over winter and so on.
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Old 27-01-2020, 19:14   #3
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Re: Babying a diesel engine

In other words:

Regular operation at normal temperatures, regular maintenance, keeping the engine CLEAN and regular cleaning of the raw water circuit will go a long to ensuring a long engine life.

Irregular low hour unloaded operations (i.e. running cold), no maintenance and never looking at the engine until it won't start will kill the most robust engine is short order.
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Old 27-01-2020, 19:49   #4
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Re: Babying a diesel engine

My little Yanmar is actually brand new, never even touched once delivered from the factory.I brought it from a guy last year who was building a yacht that never got finished......
I have since done 90 hours and itís running sweet I am still even using the impeller that was installed when the motor was assembled.
But just lately I have been motoring at 3000 rpm for an hour or two and wondering what the long term consequences would be. I am big on maintenance and agree I see more dead engines from sitting around than anything else.
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Old 27-01-2020, 20:17   #5
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Re: Babying a diesel engine

From what I have been told by my buddy the diesel mechanic (45+ years of experience) it is the low load and/or lower than specked temps that make the diesels run rougher in the long run. According to him if one has only 2 choices, 5-10F degrees over the specs is better then 5-10F degrees under. Sounds counterintuitive but he swears by it saying the higher temps help keep the carbon build up away.
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Old 27-01-2020, 20:31   #6
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Re: Babying a diesel engine

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Originally Posted by Island Time O25 View Post
From what I have been told by my buddy the diesel mechanic (45+ years of experience) it is the low load and/or lower than specked temps that make the diesels run rougher in the long run. According to him if one has only 2 choices, 5-10F degrees over the specs is better then 5-10F degrees under. Sounds counterintuitive but he swears by it saying the higher temps help keep the carbon build up away.
Iím in this boat as well, diesels like to work. That and use quality fluids (too factory specs) throughout and change them (and filters) regularly.
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Old 27-01-2020, 21:14   #7
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Re: Babying a diesel engine

I usually run mine at 2500 or so as that's where the sweet spot my particular boat seems to like.

I believe Yanmar recommends the optimal operating RPM to be somewhere in the range of 2700-2900, and to oscillate the RPMs occasionally every hour or so during periods of prolonged motoring, and to occasionally open WOT for short periods of time.

I rev the engine quickly in neutral after cool down to try to blow out any carbon deposits out of the exhaust system.

The exhaust mixing elbow should be treated as disposable and requires changing every couple years. I just did a swap out after 5 years (~500 hours) and it was very nearly completely blocked up with carbon deposits. Telltales for me were seeing some black smoke at higher RPMs and black deposits on the transom from partially unburnt fuel. I was also seeing a bit of oil consumption at higher RPMs.

Run it and give it clean fuel, air and oil and i'd wager you'll have zero issues. It's a great engine.
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Old 27-01-2020, 21:44   #8
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Re: Babying a diesel engine

Quote:
Originally Posted by Fore and Aft View Post
My little Yanmar is actually brand new, never even touched once delivered from the factory.I brought it from a guy last year who was building a yacht that never got finished......
I have since done 90 hours and itís running sweet I am still even using the impeller that was installed when the motor was assembled.
But just lately I have been motoring at 3000 rpm for an hour or two and wondering what the long term consequences would be. I am big on maintenance and agree I see more dead engines from sitting around than anything else.
Cheers
I'm sure it is sweet engine (I do like the small Yanmars ) but it was last manufactured in 1983...much newer than my YSE which ceased production '76.

Unless of course, it is a 2GM20F!
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Old 27-01-2020, 21:56   #9
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Re: Babying a diesel engine

While looking up something else came across this little jewel about low-load operation in a MAN 'Project Guide'.
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Old 28-01-2020, 07:15   #10
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Re: Babying a diesel engine

Pretty much any engine (gas or diesel) has a range in which it's happy. As long as it's loaded enough to keep combustion and coolant temps high enough for it to run cleanly, you're ok on the low end. On the high end, as long as you stay below the engine's comfortable limit for max continuous output (except for short bursts), you're good.

Different engine designs will have max continuous output at a different proportion of their max output. Running above max continuous for extended periods will shorten engine lifespan. Personally, assuming the boat is propped correctly, I like to see an engine sized so that normal cruise is somewhat below max continuous (but not way below), leaving a bit of headroom to bump the power up at times when needed without getting into the range you can only sustain for a few minutes.
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Old 28-01-2020, 08:00   #11
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Re: Babying a diesel engine

My brother and I talk about this a lot. He has owned a large construction company for thirty years and has dozens of pieces of heavy equipment with diesel motors. He runs his diesels the way they need to be run to do whatever they need done. He has never had a diesel engine that had a major failure. Usually they will go the life of the machine with nothing but oil and filter changes.

His viewpoint, is that diesel engines are not nearly as delicate as we boaters generally seem to think they are.
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Old 28-01-2020, 08:31   #12
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Re: Babying a diesel engine

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Originally Posted by jimbunyard View Post
While looking up something else came across this little jewel about low-load operation in a MAN 'Project Guide'.
diesel engines are rated by duty cycle ...load rating

Continuous duty industrial engines..load rating 100... can run continuously at 100 , full load, and achieve the designed service life

Typically a pleasure boat diesel is load rated at 30
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Old 28-01-2020, 08:39   #13
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Re: Babying a diesel engine

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Originally Posted by rslifkin View Post
Pretty much any engine (gas or diesel) has a range in which it's happy. As long as it's loaded enough to keep combustion and coolant temps high enough for it to run cleanly, you're ok on the low end. On the high end, as long as you stay below the engine's comfortable limit for max continuous output (except for short bursts), you're good.

Different engine designs will have max continuous output at a different proportion of their max output. Running above max continuous for extended periods will shorten engine lifespan. Personally, assuming the boat is propped correctly, I like to see an engine sized so that normal cruise is somewhat below max continuous (but not way below), leaving a bit of headroom to bump the power up at times when needed without getting into the range you can only sustain for a few minutes.

I think this is all correct.


Note however that the higher the load and RPM, the more wear. The optimum load and RPM in terms of engine life is probably the lowest load and RPM which adequately heats the combustion chambers. A variable pitch prop is useful for this, because a fixed prop uses less and less of max available power as RPM's fall, and at some point you do get into the range where a lot of air is flowing through the combustion chambers but little fuel is being burned and so the combustion chambers are too cool and you get problems.


Note also that your engine will "talk" to you. Certain RPM and load conditions sound sweeter and smoother than others -- that is meaningful.



When motoring for longer distances I usually run my Yanmar (100hp turbocharged 4JH3HTE) at 1700 to 2300 RPM. I follow the Yanmar instructions and run up to redline every few hours to blow out any soot or deposits.
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Old 28-01-2020, 09:09   #14
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Re: Babying a diesel engine

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.......
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Old 28-01-2020, 10:07   #15
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Re: Babying a diesel engine

I have been a diesel mechanic my whole life - (45 years experience and counting) I have worked on big ones (500 hp), little ones and everything in between-stationary, off road/ agricultural/over-the-road trucks and most recently (25+ years)numerous brands of marine DIESEL engines. I maintain and repair diesels and do many re-powers each year - mostly in sailboat service. NEWS FLASH - We KILL them with KINDNESS ! Think about how a diesel engine operates in generator service - starts up cold - governor take it right up to it designed RPM -(very close to designed MAX rpm and out of your control) before oil press. barely gets up and no load -they scream wide open and last 20,000 hours + before re-con (not replacement). I teach Diesel maintenance courses and tell people - don't baby them - "drive it like you stole it " Clean air, clean fuel, clean oil - run as close to max operating temp (but not overheat) and they will last indefinitely.
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