How long can you run a diesel engine without a load

[gary3029]

Everything I have read says the quickest way to kill a diesel engine is too run it not under load. I know it is very subjective but I was wondering how long you can run without being under load before you run the risk of damage. The reason I ask is sometimes I go down to the boat but I am not taking her out. However I would like to run the engine just to circulate the oil and remove moisture. Does the same theory apply to a diesel car? I seem to be doin a lot of standing in traffic with the engine running not under load!

 

[cliff]

10,000 hours at least at a rough guess. Personally I don't hold with the rumours that running a diesel off load will kill the engine. A good thrash occassionally will soon clean out any carbon buildup. Modern fuel and lubricants are suppossed to minimise or even prevent glazing. I really cannot see what all the fuss is over - In my opinion it is just another yacht club bar myth like heating stainless steel with a hot air gun to open the pores in the stailness steel before applying primer paint.

Having said that I usually leave the boat in gear if running alongside for battery charging or just warming it up. (seems to warm up faster under load). /forums/images/graemlins/smirk.gif
Sitting back now waiting for all the ex-spurts claiming I will kill my engine if I don't run it under load.
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"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

 

[BruceDanforth]

Why not just put the engine in gear, give it a modest amount of revs and let your warps take the strain, assuming a marina berth? As long as you are adequately fendered it shouldn't be a problem. If you are on a mooring you could try putting her astern and lay off the buoy.

 

[jax]

Does an alternator not 'load' the engine sufficiently?

 

[FlyingDutchman]

The reason you want to run the engine is to circulate the oil and to remove moisture.
The oil will circulate but you will get more moisture then before because the burning of the fuel will give off moisture. The moisture will only get out gradually if you run the engine for a longer time under load (say 30 minutes or so).
This means that if you start the engine and let it idle for a while you will do more damage than good because when you stop it and go home you will leave your beloved diesel nice and wet internally...

 

[Birdseye]

[ QUOTE ]
In my opinion it is just another yacht club bar myth like heating stainless steel with a hot air gun to open the pores in the stailness steel before applying primer paint.


[/ QUOTE ]

I've heard a lot of boll*cks but I've never heard that one! Are you sure you didnt make it up?

 

[sarabande]

If by moisture is meant "water", then so long as the engine oil runs above 100, then water will be evaporated, whether the engine is under load or not ?

Our diesel runs at about 80degrees C on the cooling side, but I haven't the foggiest idea of the temperature of the engine oil. Anyone any suggestions please ?

 

[cliff]

[ QUOTE ]
I've heard a lot of boll*cks but I've never heard that one! Are you sure you didnt make it up?

[/ QUOTE ]How dare you! Me? Make something like that up? - check out the thread a few down on priming a stainless steel rudder. /forums/images/graemlins/smirk.gif /forums/images/graemlins/grin.gif
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"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

 

[vyv_cox]

About 50 - 60 deg C would be typical for a constantly running engine under load. Evaporation may not take place but condensation in cooler areas often will, thus the sludge that forms in the rocker cover. Positive crankcase venting helps a lot and modern lubricants will absorb water to some extent.

The problem with brief periods of running is that oxides of sulphur are formed during the combustion process. These combine with the moisture produced by combustion to form sulphuric/ous acids, typically in the top ring area. Corrosion then takes place over a period of time. It is much better when winterising an engine to turn it off when thoroughly warmed up, then leave it alone until the start of next season. The practice of starting it in the winter to 'check everything is OK' is the worst thing you can do for it. The amount of water that will accumulate in the stationary engine is minute and will do absolutely no harm. Years ago there were additives that could be added to oils in engines that were to be left for extended periods. These are now pretty much obsolete as modern oils can do the job on their own.

 

[Stoaty]

If your thinking about using oil additives read this

 

[hairbox]

The fact of the matter is if you don't run the engine under load the engine will not I repeat will not ever never ever reach it's working temperature therefore the water acids etc will not burn off ha ha ha

 

[Lakesailor]

I agree with Cliff ( a first time for everything),
Diesels are used for plant machinery, indeed a lot of marine diesels are plant engines, and a lot of plant idles for a lot of their working life. Other plant runs very light loads (think about traffic lights generators). Many compressors run for ages without load. I don't imagine as a boat owner you will ever run your engines as badly as many plant operators do.
I think, as has , been suggested (and it's true for any engine) it's important for the motor to become thoroughly warmed through so that the acids and water that are produced inside are completely burnt off.
I wouldn't imagine that boat engines have any problem at all, as once under way they are under heavy load constantly. You can't freewheel in a boat.

 

[supermalc]

The reason modern engines need to be run under load is because chrome rings can glaze bores, with the result the engine will smoke and use a lot of oil. I first became aware of this a few years ago, when a friend with a garage fitted a reconditioned engine to a small van. Another friend (sadly deceased) who was a tractor mechanic, also had the same problem after fitting pistons and liners. He told the farmer to work the tractor, but he left it idling for some time to 'run her in'.

80% of engine wear is in the first 10 minutes before the engine reaches operating temperature. The best way to protect your engine is to run to operating temperature, change the oil, filters etc. then leave standing with the proper mix of antifreeze in the cooling system.

 

[Guest]

True ... diesels like to work .............

BUT the average boat engine really sees nothing like the work-load of average shore-side diesels of same build etc. Damage IMHO is usually due to salt-water / corrosion etc. rather than actual wear from running .....

The life of a diesel on a boat ?? Years and Years !! The engine I fitted in replacement of old seized engine (due to water getting into bores .... after boat flooded) ... was taken out of another boat .... touch smoky and lazy starter. Fitted .... given a real good thrashing flat out a few times ... Result > I shall not be changing my engine again !! Runs a dream. Age ? about 30 yrs ~ I often run her alongside to charge up batterys / give her a warm through etc. etc.
I'm no mechanic .... but engines fine !

 

[cliff]

[ QUOTE ]
I agree with Cliff (a first time for everything)

[/ QUOTE ]Git! /forums/images/graemlins/tongue.gif /forums/images/graemlins/smirk.gif /forums/images/graemlins/grin.gif
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"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

 

[ro8turn8ull]

Well I'm blowed !! Great piece of research very well written.Thanks Stoaty for hooking this link.

 

[Guest]

The Oil Additive page ...

As a PetroChemical lab owner ... I can say IMHO that the site is pretty well spot on ... again I say IMHO ... as we do not inspect or analyse engines.
But the point about various components being added to oils by producers is correct. Adding further of a shelf is not advised ... IMHO

BUT let me say one thing ... the page is atlking about Lubricating Oil Additives ............ yes I have commercial interest in additives in all petroleums - but they are industrial and the ones that Producers use - ... the point is FUEL additives are specifically NOT mentioned there ... and should not be confused with Lub Oil Adds ...

Just thought I'd mention it !!

 

[oldharry]

Re: The Oil Additive page ...

Most of what has been said about condensation is true - lightly loaded engines can suffer badly from condensation, leading to premature failure. Off load, a diesel may take hours to warm up to working temprature throughout. An extended thrash at or near full throttle will do a lot to put things right, but if water, sulphur and acids are allowed to remain they will attack the engine internals and cause premature failure. Valve springs are for example very prone to failure if condensation remains on them. The head may develop local hot spiots, and become distorted leading to gasket failure. Acids and other contaminants in the lube will attack bearings and journals - and so it goes on.

Industrial plant engines are designed to cope with extended periods off load. Also they will be running 8 - 10 hours maybe even 24 hours a day, so they do get thoroughly warmed up and remain so.

Its not the running that does the damage, it is what happens after shut down. If moisture and contaminants are present, and in a marine diesel they will be present in an engine that has been left running off load for an hour, then as the engine cools, they will attack.

Odd bouts of no load running - like waiting for the lock at Chi marina, will do no harm at all. Firing the engine for 20 minutes in winter to 'warm it through' then leaving it standing idle for a month, is the worst treatment of all!

Bore glazing is not a myth, it does happen, generally on diesels that never have to work hard. So going easy on the throttle to 'save the engine' is again not a good thing.

Road vehicle diesels have a very different sort of life to their marine counterpart. It is subjected to widely varying degrees of load, is in regular frequent use, and rarely stands idling more than 10 or 15 minutes (except on the M25 of course!).

But even DERV engines will suffer from under use - as I have commented before, mine hates commuting (so do I!), and needs a good hard Motorway thrash every 2 -3 weeks to get it back on top line. Good excuse to go and see the grandchildren!

 

[sarabande]

A new excuse for going down to the boat:

"Excuse me, dear, I must just go and sort out my oxides of sulphur, and the glazing on the rings. Won't be more than a couple of hours."..!

Many thanks to all the tech guys for the info; we'll just have to use the boat more frequently and for longer periods; that's all.

 

[Allan]

I've seen this said a number of times and I'm interested to hear why chrome rings would glaze bores more if not under load? I should add that I would avoid leaving a diesel engine runnig not under load, as a number of people I respect have told me it causes problems.
Allan