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Old 28-01-2020, 18:02   #31
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Re: Babying a diesel engine

Given modern electronically controlled fuel injection with just the right amount of fuel for rpm and engine load, carbon buildup should be relegated to ancient history along with the idea that you need to "blow out the carbon".

Run your modern diesel (mine are twin Cat 3406Es) at normal operating temperatures (mine 180 F thermostats) at any rpm (mine about 1200 for 8-9 knots at 20 gph) and enjoy modern technology and quit fretting about what percentage power to run when.

Oh, while not a diesel my race car engine has similar moving parts. Run it 500 rpm short of it's 7500 rpm redline and you could double the life of the engine from 30 hours between overhauls to 60. Says a lot about not abusing or maybe using equipment.
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Old 28-01-2020, 18:27   #32
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Re: Babying a diesel engine

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Originally Posted by Squanderbucks View Post
Most Diesel engines come in various setups for the same engine block at different hp ratings. These ratings give specifications about what power output should be done. Example. Full throttle not more than 2 hours out of 8 running. Or not above a certain rpm for mor than 8 hours out of 24. ETC.
but basically if you prop the boat right do it is able to achieve at least 100 rpm OVER the rated WOT setting then you should be able to run the engine at any speed you want up to around 80% or do indefinitely. WOT occasionally if needed for short bursts. But definitely Not lugging along at 1100-1200 for long periods. Also best way to kill a diesel is to Over Prop it not allowing it to achieve top rated RPM.
I have seen this claim a few times but I can't understand how you prop the boat to achieve an RPM that is above the engine manufacturer's rated maximum. Does not the engine governor limit the max RPM at WOT. It always seems that even in neutral (i.e. no load) and WOT, the max RPM is limited by the governor.

What am I missing here?
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Old 28-01-2020, 18:31   #33
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Re: Babying a diesel engine

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Originally Posted by Wotname View Post
I have seen this claim a few times but I can't understand how you prop the boat to achieve an RPM that is above the engine manufacturer's rated maximum. Does not the engine governor limit the max RPM at WOT. It always seems that even in neutral (i.e. no load) and WOT, the max RPM is limited by the governor.

What am I missing here?
It depends on the engine. Some have the governor set 100 - 200 rpm higher than the spec-ed WOT RPM, so you can let it turn 100 RPM above spec. Or they give a spec-ed range for WOT, so you aim for the top of the range. If it's governed right to WOT RPM, then you can just prop it so it's at slightly less than full fuel to achieve governed RPM.

Basically the idea is to leave a little headroom so that you don't end up overpropped if the hull gets a little dirty, etc.
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Old 28-01-2020, 18:35   #34
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Re: Babying a diesel engine

Even common rail is still a Diesel, and Diesel soots, it’s just the way it is, ask VW. Clean burning Diesel is a contradiction of terms, sure it’s exhaust can be cleaned up, but it’s hard, and expensive to do.
An “Italian tune up” every once in a while won’t hurt, and can help. For one thing in my opinion run the snot out of an engine once in a while and watch the temps closely, if they climb higher than normal, that’s telling you that your cooling system needs maintenance. You’ll exceed it’s reduced capacity at high power output, but won’t running around at low loads and finding out that your cooling system needs attention before the engine overheats is a good thing.
Of course if you stick to a maintenance schedule your cooling system should always stay good.

I just don’t believe in the run it like you stole it, or Diesels thrive at being run hard thing, but running one hard for 5 min every now and again doesn’t in my opinion hurt one.
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Old 28-01-2020, 18:42   #35
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Re: Babying a diesel engine

If you look at the propeller power curve as opposed to the engine power made curve you’ll notice that we should really all over prop by a considerable margin, IF and that’s a big IF we have enough sense to know to not overload the engine.
An engine that is propped so that it can reach max RPM, is pretty well under loaded at all RPM’s less than max RPM, and is one reason that we can get away with running our 3600 RPM engines at 3000 RPM or so and not kill them, because even though we think we are running them hard, we really aren’t, they are not loaded up, it’s similar to running around in a car on the highway in second gear, your turning high RPM, but not seriously loading the engine.

That’s where a controllable pitch prop would be gold, if they existed, the Autoprop tries and does a pretty good job, but it would be nice to be able to control prop pitch and therefore engine load, but that’s complicated and likely expensive, and maybe we don’t need expensive complex things?
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Old 28-01-2020, 19:27   #36
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Re: Babying a diesel engine

Quote:
Originally Posted by a64pilot View Post
Even common rail is still a Diesel, and Diesel soots, itís just the way it is, ask VW. Clean burning Diesel is a contradiction of terms, sure itís exhaust can be cleaned up, but itís hard, and expensive to do.
An ďItalian tune upĒ every once in a while wonít hurt, and can help. For one thing in my opinion run the snot out of an engine once in a while and watch the temps closely, if they climb higher than normal, thatís telling you that your cooling system needs maintenance. Youíll exceed itís reduced capacity at high power output, but wonít running around at low loads and finding out that your cooling system needs attention before the engine overheats is a good thing.
Of course if you stick to a maintenance schedule your cooling system should always stay good.

I just donít believe in the run it like you stole it, or Diesels thrive at being run hard thing, but running one hard for 5 min every now and again doesnít in my opinion hurt one.

Sadly can't argue with any of this or post about prop pitch. lol.
Our boat engine max rpm is 3400 rpm but we have it pitched so it only revs to 2400 rpm without any sail assistance. This is by accident rather than design. Eventually I will repitch so motor will achieve 2800rpm as a minimum. However I can see no detrimental engine behaviour at present EXCEPT because it is only rated to 7hp continuous we are only getting 5.5 hp out of the engine at max rpm without overfuelling & blowing black smoke.
This is a safety issue when you are trying to get out of an open roadstead anchorage at over say 25 knts with a tiny engine.
Wont apply to most CF members.
We do make sure that the engine stays below the blowing black smoke limit for 2 reasons. First you are pumping only slightly burned diesel onto the sea surface, why pollute & waste diesel? Secondly, in theory, the excess diesel in the chamber dilutes the engine oil on the cylinder wall so increasing wear on everything in the combustion chamber (+ v/v guides? ) I'm guessing at the guides part tho.
Yanmar, in the service/workshop manual says to give it a full rev run for a brief period before shutting down. I have never noticed it blowing out any crap in the marina whilst doing this so only do this rarely now
HOWEVER. our engine is naturally aspirated mechanical injection so you turbo types may well be different. Be warned.
We mostly run around 2000 rpm & the engine runs as clean as any boat diesel I've seen at 1st hand ( those would not include any common rails EFI)
despite being vastly over-pitched.
It's oil temp sits about 59oC when as hot as it gets.
To my somewhat mechanically educated ear not running hard out is fine. I just look for the sweet spot where the engine sounds happy.
However I repeat my thoughts are only applicable to naturally aspirated older diesels
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Old 28-01-2020, 20:41   #37
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Re: Babying a diesel engine

The reason commercial engines run longer at full hp is because they cost more. There are more expensive alloys in the cylinder components (sleeves, rings, valves & pistons) and can take higher temps for longer periods. Also the engines are manufactured with fast rebuilding in mind because down time is expensive for the owner. Full hp in a truck engine is less than the same engine in a boat. The truck engine is usually down rated in hp because it's harder to cool with air. Smaller injectors and maybe a different cam.

I can't speak for small engines, but for HD marine turbo engines, if you stay under 80% of hp and change oil on time, you'll probably double the life. I've seen it many times in Cats and Detroits. When I had a yard, that did mostly commercial boats, I got a number of sport fisher and puker boats for engine rebuilds. They hadn't been happy with some other people fixing their engines. The owners that kept the hp below 80% generally got double the hours of the ones that didn't. And often a rebuild was more expensive.

The other problem with high temps in turbo engines is cavitation - bubbles forming and popping during ignition against the water side. Look it up. It causes pits, making the wall thinner and more susceptible to heat damage. It can make raised areas in the actual cylinder and if not removed by honing or reboring the cylinder, the raised spots will cause the new sleeve, etc., to wear faster. Often you have to bore and install an oversized sleeve. Usually not every cylinder. And if you're followed by some barnyard mechanic in a later overhaul that installs all standard sleeves, then you have another problem.
As to over propping, almost all of my personal boats were over propped. I ran at a lower rpm, got better mileage and life between overhauls than the manufacturer advertised. When I was a fisherman, on the salmon prop I could only get about 60% of the max rpm and with the tuna prop about 80%. I had to change props to go slow enough for trolling. Otherwise I had to use drags.
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Old 28-01-2020, 22:11   #38
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Re: Babying a diesel engine

Quote:
Originally Posted by a64pilot View Post
If you look at the propeller power curve as opposed to the engine power made curve youíll notice that we should really all over prop by a considerable margin, IF and thatís a big IF we have enough sense to know to not overload the engine.
An engine that is propped so that it can reach max RPM, is pretty well under loaded at all RPMís less than max RPM, and is one reason that we can get away with running our 3600 RPM engines at 3000 RPM or so and not kill them, because even though we think we are running them hard, we really arenít, they are not loaded up, itís similar to running around in a car on the highway in second gear, your turning high RPM, but not seriously loading the engine.

Thatís where a controllable pitch prop would be gold, if they existed, the Autoprop tries and does a pretty good job, but it would be nice to be able to control prop pitch and therefore engine load, but thatís complicated and likely expensive, and maybe we donít need expensive complex things?
You make a good point - one I must remember.
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Old 28-01-2020, 22:12   #39
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Re: Babying a diesel engine

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Originally Posted by rslifkin View Post
It depends on the engine. Some have the governor set 100 - 200 rpm higher than the spec-ed WOT RPM, so you can let it turn 100 RPM above spec. Or they give a spec-ed range for WOT, so you aim for the top of the range. If it's governed right to WOT RPM, then you can just prop it so it's at slightly less than full fuel to achieve governed RPM.

Basically the idea is to leave a little headroom so that you don't end up overpropped if the hull gets a little dirty, etc.
Thanks for the explanation.
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Old 29-01-2020, 00:08   #40
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Re: Babying a diesel engine

I run my Volvo at 2000/2100 rpm... its max RPM is in the order of 2500.
Not only do I think it is kinder to the engine I also think it may be the sweet spot when it comes to miles per litre....

My two vehicles are both diesels, one redlines at 4000 rpm... highway speed of 100 kph is 2000 rpm.. the other is 5000/2500 so not working remotely hard 95% of the time.
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Old 29-01-2020, 00:39   #41
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Re: Babying a diesel engine

[QUOTE=Lepke;3064293. When I had a yard, that did mostly commercial boats, I got a number of sport fisher and puker boats for engine rebuilds. They hadn't been happy with some other people fixing their engines. The owners that kept the hp below 80% generally got double the hours of the ones that didn't. And often a rebuild was more expensive.

The other problem with high temps in turbo engines is cavitation - bubbles forming and popping during ignition against the water side. Look it up. It causes pits, making the wall thinner and more susceptible to heat damage. It can make raised areas in the actual cylinder and if not removed by honing or reboring the cylinder, the raised spots will cause the new sleeve, etc., to wear faster. Often you have to bore and install an oversized sleeve. Usually not every cylinder. And if you're followed by some barnyard mechanic in a later overhaul that installs all standard sleeves, then you have another problem.
As to over propping, almost all of my personal boats were over propped. I ran at a lower rpm, got better mileage and life between overhauls than the manufacturer advertised. When I was a fisherman, on the salmon prop I could only get about 60% of the max rpm and with the tuna prop about 80%. I had to change props to go slow enough for trolling. Otherwise I had to use drags.[/QUOTE]

Interesting post to me anyway Lepke thanks.
Just need a translation of puker boats. Thought I was schooled in American vernacular one but that escapes me.
My guess is it's top heavy launches but please enlighten me.
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Old 29-01-2020, 10:50   #42
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Re: Babying a diesel engine

There are plenty of good diesel engines used in 60hz generator applications that operate at 1800 RPM continuously, for the entire life of the engine. These generators see many thousands of hours run time. These same engines are used in propulsion applications with variable speed.

If an engine has to be babied and coddled and 'blown out' on a regular basis, just to keep it running; that's a design problem with that engine and not indicative of all diesel engines.

Likewise, good quality diesel engines are used in 60 hz generator applications where the engine is run at their maximum governed RPM of 3600. Continuously, for the life of the engine. They also see long service.

A quality diesel engine that is not overloaded, should be able to be used anywhere within its operating RPM range and not cause it harm or maintenance issues.
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Old 29-01-2020, 11:03   #43
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Re: Babying a diesel engine

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Originally Posted by a64pilot View Post
If you look at the propeller power curve as opposed to the engine power made curve youíll notice that we should really all over prop by a considerable margin, IF and thatís a big IF we have enough sense to know to not overload the engine.
An engine that is propped so that it can reach max RPM, is pretty well under loaded at all RPMís less than max RPM, and is one reason that we can get away with running our 3600 RPM engines at 3000 RPM or so and not kill them, because even though we think we are running them hard, we really arenít, they are not loaded up, itís similar to running around in a car on the highway in second gear, your turning high RPM, but not seriously loading the engine.

Thatís where a controllable pitch prop would be gold, if they existed, the Autoprop tries and does a pretty good job, but it would be nice to be able to control prop pitch and therefore engine load, but thatís complicated and likely expensive, and maybe we donít need expensive complex things?
Iíve sailed with several controllable pitch props .. hundested

Beautiful equipment that allows you to fine tune prop pitch to operating conditions

Shame that small size units seem to be no longer produced

Iíve also used the auto prop..not impressed

The MAX prop or its imitations seem to be the best for sailing boats
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Old 29-01-2020, 12:39   #44
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Re: Babying a diesel engine

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Originally Posted by FPNC View Post
There are plenty of good diesel engines used in 60hz generator applications that operate at 1800 RPM continuously, for the entire life of the engine. These generators see many thousands of hours run time. These same engines are used in propulsion applications with variable speed.

If an engine has to be babied and coddled and 'blown out' on a regular basis, just to keep it running; that's a design problem with that engine and not indicative of all diesel engines.

Likewise, good quality diesel engines are used in 60 hz generator applications where the engine is run at their maximum governed RPM of 3600. Continuously, for the life of the engine. They also see long service.

A quality diesel engine that is not overloaded, should be able to be used anywhere within its operating RPM range and not cause it harm or maintenance issues.
Said generators often run continuously, only being stopped and restarted for servicing. This dramatically reduces wear and increases the service life when measured in hours of operation.

The marine or mobile equipment versions will often have higher hp ratings and be restarting from (near) cold every few hours. Both have the opposite effect.

Just look at the service life of taxis vs cars that only see half hour trips to the shops/school.
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Old 29-01-2020, 13:48   #45
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Re: Babying a diesel engine

When running pretty much every moving part except the rings float on a film of oil. The only time metal actually touches metal is at startup. No wonder gensets live so long.
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