Diesel engine care

[cpedw]

In another post, Vyv Cox wrote "My personal choice is to run my engine towards the bottom end of the rev range, with occasional high-rev bursts to keep the engine sweet."
I've heard something similar elsewhere so I'm sure it is true. Can anyone give guidance on how frequently the high rev burst should be applied and for how long? In case it matters, I'm interested in a 20 year old VP2003 that seems to run OK at the moment though it has had cooling problems in the recent past.
Thanks,
Derek

 

[jerryat]

Oh I know how you feel! The guys at Bukh Diesel (my engine) always 'moan' because I'm loath to blast along at full throttle for long periods 'in case I damage the engine'!

They fall about laughing, ponting out that they are designed to run 24/7 at near flat out, but I still find it hard to do. My 'compromise' is to run at or near flat out for around 30 minutes a time (perhaps three times a month) but I have no real idea why. I understand the risks of polishing the bores if there is no load, for example when at anchor and charging batteries, but surely motoring along at even a couple of knots is 'under load' isn't it? /forums/images/graemlins/confused.gif

Perhaps someone on here can provide a definitive answer, or least an idea of the actual benefits. /forums/images/graemlins/confused.gif /forums/images/graemlins/smile.gif

 

[VicS]

[ QUOTE ]
a definitive answer

[/ QUOTE ] There is no definitive answer. I'd go along with Vyv Cox.

 

[Phoenix of Hamble]

Last year, I did an 100nm passage with absolutely no wind at all..... however the forecast wasn't looking great, so I wanted to get a move on.... so I motored the whole way at higher revs than I normally would..... ie gave the engine a good 12 hour thrashing!

It was noticeably smoother and quieter after this!!!!

So i'm in the give it a good hard run every now and then camp.

 

[jwilson]

Diesels like work, hate prolonged low revs/load. Like long runs, don't like short periods of running.

Your typical modern yacht auxiliary is based on an industrial engine block that is designed and built to run non-stop for days or weeks on end at highish revs/load powering a generator or compressor.

 

[gwc2004]

I have always been told by a marine engineer friend that diesels need to work. He says that a large engine working at low output won't last as long a a smaller engine developing same output but having to work harder. I have a Volvo 2002 in my boat and it likes to run at around 2200 rpm. It will rev higher but you learn the comfort zone of any engine. If it's set up and maintained properly it will do what the manufacturers say it will.

 

[jimbaerselman]

Diesel engines are designed to run for long periods near the peak of their torque curves. Generators run for tens of thousands of hours close to peak torque.

Rpm governors are set by manufacturers a little above the peak torque for leisure vessels - more power can be advertised! The identical engine sold commercially may have a 10% lower governor setting - more life can be advertised.

The 'maximum continous' rpm should be quoted for your engine. There should be no problem using this if you've got a well matched transmission and prop system. Unless it's inefficient to try to go so fast!

However, if, at max continuous revs, you get black smoke, there is a problem. Assuming the injectors are OK, the vessel is probably over propped and is being overfuelled. Reduce revs/throttle until the black smoke stops.

No, don't teeter around at low revs all the time, you will glaze the cylinders and create long term compression problems. Get a smaller engine instead /forums/images/graemlins/tongue.gif

 

[pampas]

The "Best" loading is about 75% of its POWER range,thats the range deep sea we would start another generator, best for wear and tear and fuel efficiency. Seemed to be the rule in all of the ships that I served in. The only diesels that suffered were the instant start emergency alternators which were tested once weekly running at full speed and no load. Personally I have stuck to this practise when making passage battery`s during weekend forays get low so a bit of low power running will not hurt. In 10 years with the same engine she smokes a bit not much oil burnt and the bore still looks good,Wrong time of the century to recomend fuller throttles,when everybody is shouting "Save it".

 

[doug748]

"Save it" indeed. I can go sedately at 2000 RPM or get an extra knot, plus noise and double the fuel consumption at 3200. I don't know if the lower speed will impinge on the efficiency of the engine in the long term, I rather doubt it. Running at tickover for charging might be a different matter.

 

[johnalison]

The instructions on my Volvo 2030 say it should normally be run at 4-500 rpm below maximum revs which for me is 3,400. Tanking along at 3,000 rpm isn't my cup of tea and the most I've done is 24 hours at 2,700 which was hard enough.

 

[Heckler]

Lots of urban myths and fairy tales, look at life in general, diesel engined car, do you worry about driving slow, fast or what ever? Industrial engines? define industrial!! designed and built to do industrial, WTF does that mean? The VP MD22 was designed and built by Perkins, fitted to Montegos and god knows what else, is that an "industrial" engine?Generators run at certain rev ranges to suit the generation characteristics not to suit the engine!! The black cab is a good example, engine switched on and not switched off till end of day allegedly, if it is ticking over for most of the time, so what?
Dont think about the damned thing, use it to get from A to B when necessary, change its oil and filters and it will last for ever.
Stu

 

[Steve_N]

[ QUOTE ]

Dont think about the damned thing, use it to get from A to B when necessary, change its oil and filters and it will last for ever.
Stu

[/ QUOTE ]

Ahh a man after my own heart. Engine longevity comes way below comfort while motoring and fuel economy in my book. If I have to re-engine after 30+ years then so be it, though it will most likely have died from corrosion and not running at low output anyway.

We are over-engined: 61 BHP for our 9 or so tons.
We tend to motor at a relaxed and very enjoyable (almost soporific) 1500rpm giving just under 7kts, and reach hull speed at 2000rpm - all with an engine rated to 4500rpm.
She'll be 25 soon, doesn't use oil or coolant, doesn't smoke and starts on the first turn, so seems to tolerate it.

 

[mortehoe]

IMO, after having rebuilt hundreds of diesels - marine, car, truck ...

Those who run their diesel engines with no load fail soonest. Those who run their engines with caution fail at more or less the same time as those who run their diesels with little or no load. Those who treat their engines with total disregard and run it to get the max speed, but have it serviced & professionally maintained properly will outlast the timid users by a factor of between 5 and 10.

IE: for instance The life of a Yanmar GM10 or a Volvo MD20 should last for over 12,000 hours .... Most of the above 'fail' at over 1500 hours and are not worth rebuilding (ie ALL marine diesel manufacturers have loaded the price of new/spare parts such that it is most-times cheaper to buy new ... and we are talking here even in the economy class of having to spend £3,500+ all up excluding VAT, beer funds and other stealth taxes to renew/replace an engine .....)

The best way to run your diesel is to treat it like a whore: run it hard and service it 200% regularly: ie You are able to get a small marine diesel to outlast you but the Yards and the Manufacturers are conning you into thinking that a small marine diesel is only good for 10 years or 1200 hours whichever is the less ..... If you know how to use a digital micrometer, a proper spanner, a silver steel scraper, wire brushes, a few other off the shelf other things and a torque wrench then you can do it yourself and stick 2 fingers up the Yard's so called professional engineers who are all for getting their commission for less work by installing a whole new (sharp intake of breath) engine propshaft stern gear and prop than for restoring what you have.

Phewwww ... But it's true. We are all being ripped off by Yards who tell us intake-phwewwwww "It's gorrabee a new ....." rather than "Yes it can last another 20 years, and here's a good way to do it ...."

 

[vyv_cox]

Re: IMO, after having rebuilt hundreds of diesels - marine, car, truck ...

The Yanmar workshop manual advises to run the engine at full revs for five minutes every two hours. It doesn't differentiate between running at low revs for battery charging or cruising revs, maybe half to two-thirds maximum.

There is little doubt that running at low revs for long periods leads to performance reduction that is cleared by running flat out for a time. I have personally witnessed a certain yard charge £100, at least 10 years ago, for providing this service. Needless to say, the owner was not aware how his engine's good performance was restored.

 

[wanderlust]

I have a Yanmar 3HM35. We run it pretty hard compared to everybody else Ive read above. It is rated to run at 3200rpm continuosly and 3400rpm for an hour according to the book.
We generally run at about 2800rpm and if we are in a hurry I have no problem with running at 3000rpm all day. The engine is not much noisier at high revs than low revs. Being a catamaran the extra revs mean extra speed so it works for us to rev it. The engine was stripped at 12 years old for an inspection and it had no measurable wear. We cleaned out the water ways cos they were pretty blocked (raw water cooled engine). The engine was put back together and has since done 1300 hours trouble free. Marine engines rarely fail due to being worn out. Usely lack of maintenance and lack of use. Give it some stick!

 

[Stemar]

Re: IMO, after having rebuilt hundreds of diesels - marine, car, truck ...

Jissel is grossly overpowered with her 28hp VP2003 in a 24ft bilge keeler, so I rarely need more than about 1/3 throttle. I find that the engine gradually gets smokier and harder to start over a period of a few weeks, so I give her a good blast at 6.5 knots - around 90% of full throttle, and well above hull speed - for a couple of miles. I try to choose a windy day, cos otherwise, when I start, I look like a WW2 destroyer laying a smokescreen, but after a couple of minutes, the smoke goes and all is well.

My recipe for a long life is a good blast now and again and basic servicing more often than the book says. Works pretty well for engines, too...

 

[Marsupial]

All I can add is that “industrial” engines used to run at lower revs than “leisure” engines – but the difference is hard to define now and as all engines are made to tighter tolerances, clean oil and regular maintenance makes more difference to expectancy than the grade of engine (but Yanmar still have grades AFAIK their marine engines are designated leisure engines with a 200 hr a season duty (14000 miles on a motorway)). Back when dinosaurs roamed the earth and I worked in diesel engine testing, diesels were very heavy and were governed to 1800-2100 rpm because if they did 3000 rpm for any length of time a big piece of metal fell off! A high speed diesel did 2400 rpm. Thankfully they are better now and 3800 rpm is commonplace if not a bit slow.

Direct cooled engines will tend to wear out quicker because they tend to run cooler this is because operating temperature has a lot to do with engine life.

However, if we assume that everything is correctly sized, ie the prop is the correct size for the engine (and not sized some other way that makes it the correct size for the boat – yes it happens) then running any engine on a light load will shorten its life. The bores will glaze; the engine will eventually loose compression and efficiency will suffer. The combustion chambers will not scour correctly and carbon deposits will build up on valves, piston rings and injectors and the thing will become difficult to start. Oil will not get hot enough to drive out moisture and the engine will become contaminated by condensation, internal corrosion will increase. Cold oil is not very good at “washing” carbon partials away from bearings and rings so they will tend to wear more rapidly.

Light loading a diesel is a very bad idea. Note that river boats often have two sets of props so when going slowly in rivers the fine pitch is fitted so the engine will rev a little harder when on a light load to try and counter some of the negatives above – but its still a bad idea.

The message is clear to get the maximum life from an engine you must set it up right, keep it well maintained and run within its maximum torque rev range usually between 60 – 80% of stated max continuous rev at operating temp for an hour or so at least.

I am writing this in a KIA taxi that has done 500,000 miles and is still on its original engine but some of the ancillaries are “new” – according to the driver this is not exceptional but he changes the oil every 5,000 – but then there is a lot of it about out here and engines are almost at operating temperature as you start them up most of the time. Current temp in the shade struggling to reach 42C summer is on its way.

Cheerio from the Sand Pit for another week

 

[boatmike]

There is no definitive answer. I'd go along with Vyv Cox.
___________________________________________________

Actually Vic there is a definitive answer but it is not as simple as most people think.
If you look at the technical details of the engine spec it should give you the rating under two headings. "Continuous" and "Intermittent"
Engines based on industrial units like Mitsubishi and Peugeot have a continuous rating that is very near to maximum power rating. Note that MPR is not "flat out". All power curves will give increased RPM above this point but with vastly increased fuel consumption without much increase in power. The MPR is the RPM that manufacturers of diesel gennies and other similar kit use, usually less about 10% for safety. Engines designed specifically as "Leisure Duty" are far less robust and lighter built units where the continuous rating may only be about 70% of MPR which is where you get the Yanmar thing about "run me at 2500 RPM but give me 5 minute bursts of MPR every hour".
Therefore marinised heavy duty truck engines are best run and happiest at near MPR and will last a lifetime if used like that. Little Yanmars should not be hammered quite so hard, but should be given occasional bursts of high throttle.
Running at low RPM will cause excessive carbon deposits, bore glazing, and other problems, especially if only used for short periods.