Care of your Diesel Engine

[Chris_Stannard]

For years I have run my engine at sensible cruising revs about 2500rpm, and thought this was best for longevity. I recently changed boats and now have a Yanmar engine. I had to speak to the Yanmar technical helpline and was advised that, to give my engine the best treatment I should run it flat out for about 20 minutes before I come into harbour. This gets rid of the carbon etc. build up in the valves and so on and helps to keep the engine running sweetly.
Being a 'Doubting Thomas' I checked this advice out with my local, and very good diesel man. He confirmed it, so that is what I will do in future. So at 64 that's something I did not know, and thought that some of you might appreciate the tip also.

Chris Stannard

 

[ParaHandy]

I know that you're right but instinct takes over as the mechanical monstrosity reaches 3500 revs and every untoward vibration has you twitching over the throttle ready to yank it back to a more leisurely pace!

 

[billskip]

How does the guy with one of these engines in his boat on the thames manage?
"sorry guv but I was doin wot the instructions says" or are these engines only fitted to boats for unrestricted waterways?...

Bill
www.aegeansailing.co.uk

www.macsyachting.com

 

[brian_neale]

Is it reasonable to assume that the throttle stop and/or governor on the engine will stop it exceeding max revs, having been set by the engine manufacturer, and whether the engine is underpropped or not? I keep hearing people say that diesels should be worked hard, but it goes against the grain to do it!

 

[billskip]

agreed Brian..I cant see a guarantee being honoured if you told the makers "I thrashed hell out of it for 20 mins and it broke". ..people still tend to make statements of theory that are just not practial..imho.an answer to my question " how does a boat on restricted waterways carry out this proceedure? is there one?

Bill
www.aegeansailing.co.uk

www.macsyachting.com

 

[JeremyF]

This must explain why returning back to Port Solent we were overtaken 3 times by powerboats exceding the 10 knot max in Portsmouth harbour, chucking out vast amounts of wash.

Their excuse ? "Not my fault, my engine manufacturer told me to do it!"

Seriously, I doubt that the advise is good for turbocharged deisels. They like 20 mins of non-boost before shutting down.

Jeremy Flynn

www.yacht-goldeneye.co.uk
New pics 11.02.02

 

[ParaHandy]

Yep, it\'s Monday morning

Come on...I think he's got something like a 3GM (as do I) which at max revs will do abt 6.5kn with following wind etc etc. Taking it all a bit too literally?

There's a long thread over in Motor boats confirming this and the Yanmar USA engine site says the same. No idea what Thames boats do, probably can't.

I've not got the bottle to stand it for 20mins. Just feel the little b*stard will croak on me.

 

[yoda]

Just to add my experience to the debate, as a marine engineer routinely dealing with both normally aspirated and tubo charged engines I offer the following: Diesel engines in general are not happy with working on light loads. Neither do they like to be shocked so thumping them from a light load up to max chat is not going to do any good either. Most of us keep our boats in places where going full chat at the end of the home run is probably not acceptable. Perhaps a compromise is in order here. Don't be afraid to run the engine upto full power, that is why there is a rev limiter fitted. It will do the engine good but it is worth being gentle and working it up there over a few minutes to let everything warm through at the same rate. If however the last 30 minutes or so of the day you have to slow down then that is the way it is. Next time you are out in the open give it a good run to clear it out. In my opinion the worst thing for a diesel engine is being run out of gear just to charge the battery. Unless racing I would always put it in gear and let it have some load and help cover the miles. Better not to need the engine to charge battery. Long live the petrol engine - not a problem I have to put up with!

 

[romany123]

Good Post Yoda
Can I have your phone number for emergencies

Dave

 

[Trevor_swfyc]

Plenty of down sides occur to me, if the engine is salt water cooled you are parking up with the engine hot, salt water in the head not moving. Water may be boiled off leaving salt in the cooling channels which could result in early failure the complete opposite to what was intended. The stern gland is taking a bashing the faster the revs the more vibration you get, also the gear box does this like a thrashing I think not. The prop if you start to cavitate this will also be the worse for the thrashing.
Just playing the devils advocate!
Trevor

 

[seaesta]

I wouldnt want to run my MD1 at full tilt for more time than necessary.

I am not squeemish about the old knocker but it would likely shake something to bits, hole the bottom or bend the propshaft. She simply isnt well balanced enough for a regular preventive trashing. After taking the engine to 34 years service without such treatment I am not going to adopt this now.

Is this requirement/suggestion only for the more sophisticated newer "iron mainsls" and Yanmar in particular?

 

[Bergman]

Not an expert on Diesels but I can't help thinking if youv'e done it for years without a problem them maybe not mending what isn't could be a sensible move.

 

[Guest]

No engine likes to be operated at maximum power. The wear of materials is quicker, lubrication is less efficient, the stresses due to vibration are increased. All engines will clear up from carbon if they run just above the idle speed.

 

[brian_neale]

...and I do let my engine idle for a few minutes before switching off to let it cool gradually. Guess it would need a longer "cool down" time if it were thrashed going into the marina! I believe that this is specifically recommended for turbo engines to let the turbo in particular run down/cool down.

 

[Chris_Stannard]

Thanks for a comprehensive answer, which I shall follow. I certainly would not want to thrash my engine a fullchat for long periods but a short burst to clear the carbon seems to make very good sense. I take the point about the possiblity of increased wear because of high tempartures which is why I guess the engine manual says 3750 max for no more than 30 minutes and 3500 for fastest running. I always understood that the ideal normal load was 80% full power but I do not know where that occurs, probably at 3000-3200 I would guess.

Anyway many thanks for all the comments and I am afraid I do not have the answer for the Thames, except perhaps do not fit an engine bigger than you need. Its like use a 4x4 cross country vehicle for the school rum

Chris Stannard

 

[tristan]

Hi,

Not wanting to start an argument, but i think most people are missing the point here, just to echo yoda, i am also a marine engineer, and it is most definately good for a diesel engine to be run UNDER LOAD. This does not necessarily mean full chat, or 80% of that,or whatever. For example, if you were punching a 2 knot tide, and making a headway of 2 knots, then the hull speed would be up to 4 knots, which is a good cruising speed, the engine would be at about 2/3rds throttle and nicely loaded. About 20 mins. of this once every 6 months or so will see your yanmar through until the boat falls apart around it; remember, the key here is load, not revs!

To try and dispell some of the rumours:

A diesel engine, whether tubocharged or not will suffer from what we call 'light loading', this is where the engine has either been idled for extended periods, or has not been placed under load while running. This has the net effect of polishing the bores, coking up the injectors, exhaust passages and cylinder head, which in turn can lead to more problems, such as high oil consumption, poor starting, and in the worst cases the engine will 'run away', or run on it's own oil.

A diesel engine will not over-rev. Never ever unless the fuel pump has been fiddled with (like that would ever happen!!!) or unless there is a fault with the fuel system or, as previousely mentioned, it runs away. Whether the boat is light, under-propped, or over-engined, the govenor will not let the engine exceed it's no-load, or 'flight' speed, even in neutral. In fact one of the points on any manufacturers recommended service interval, is to check the low and high idle speeds (if any-one would like proof, i can back this up). Another point to note is that any engine that will not reach it's no-load speed is probably very ill, and chances are it won't last too much longer anyway.

Running an engine at high speed will not damage the gearbox. It may well damage the coupling or stern gland, if there is a lubrication or alignment problem, but provided there are no problems with the gearbox, they are rated in excess of whatever power the engine can produce to cope with the torque and thrust transmitted though the drive, and will not fail.

I hope this has shed some more light on the subject, and not confused anybody too much, and if anybody requires more information, whether specifically, or generally, please don't hesitate to ask.

Tristan.

 

[tonyleigh]

Many thanks the thought and time you put into this reply.

 

[Chris_Stannard]

Thanks for the input

Many thanks for your time and trouble. In my old boat it took the engine two seasons to need a second top overhaul, having run it to charge the battery (racing offshore) and running it lightly loaded at other times.
I just fitted a folding prop to replace a fixed 3 bladed 18x13 prop. The advice from the boat builder was fit a 17 inch. On being asked he said this came from Yanmar. I asked Yanmar who said that boats were frequently overpropped and this was not good for them. I have fitted the 17 inch as suggested but only went back in the water yesterday in strong winds so I have not yet had a chance to see what the difference is. If anyone is interested I will post a thread in middle April when I have had a chance to see what the difference is.

Chris Stannard

 

[brian_neale]

Thoughts on diesels

I was trying to think about why fast idling diesels off load was bad for them. I presume that this is because the throttle lever actually controls the governer, not the fuel supply directly (unlike most petrol engines). Off load, when you open the throttle, you are telling the governer to speed up the engine. It will end up supplying an appropriate amount of fuel (which will be very small), but the air supply will depend only on the engine speed. This leads to very weak mixture running, which presumably leads to the long-term problems mentioned elsewhere. If the engine is loaded, then there will be more fuel supplied for a given engine speed, same amount of air at that same engine speed, therefore richer mixture. I would conclude that this should be true, more or less, for a reasonable range of engine speeds if the load is appropriate. However, a prop provides a load which is roughly proportional to the square of engine speed (guessing from shape of fuel consumption curves) so low speeds even under load give significantly less than the design load and therefore too weak a mixture. Conclusion - go faster to get home before your engine wears out!

Maybe loading the engine stops bore glazing and similar problems, but does it really clean out carbon deposits?

 

[Chris_Stannard]

Re: Thoughts on diesels

Yanmar said that running the engine at full power raises the temperatures to a level where the carbon does indeed burn off. My local expert confirmed this.

Chris Stannard