diesels

[jsl]

I have heard it suggested that a marine diesel, normally run at maybe half throttle, should from time to time be given ten minutes at full blast 'to clean it out.' Is this good advice? If so, how often should it be done? Are there precautions to be taken? What will happen to a twenty-year old engine?

 

[Guest]

Old wives tale with no substance. If anything you are liable to cause damage through unusual use.

The cylinders wear over the life of the engine, and the nature of the wear is dictated by the speed at which the engine is run. Sudden hard usage can find the weakness and the problems begin.

To prolong the life of your old engine I would suggest it is better insurance to flush the old oil thoroughly (with a proper oil flushing solution) and be strict about oil changes. Many owners cease to nurture their engines once they are old.

 

[AndrewB]

More a case of the opposite ...

Don't run your engine in idle for too long, as running cold encourages carbonisation. (So fast that they chuck out black smoke/raw fuel isn't good either). Diesel engines are happiest running under load at proper working temperature.

 

[vyv_cox]

It is a fact that many boat owners turn up at yards with engines that they claim are "not running well, poor output". Standard treatment is to take the boat flat out for a mile or so, (when the owner has departed) which does have very positive effects on performance, presumably by oxidising carbon deposits, freeing up piston rings, etc. Usual result is pleased owner, lighter of pocket by 100 pounds, and delighted yard owner.

 

[BarryD]

LOL - When Renualt Fuagos Turbos (or something like that) were new and fun - a garage I know used to do this to one customers car. He did a lot of town driving and never ramped it at all. Every three / four months in it would come for a check up. Which ever apprentice was free was told to buzz off and thrash it for half an hour.

Got so the garage didn't even bother charging him.



Compliments of the season

Barry

 

[Guest]

Just like m/s car silencers

Diesel engines need to be warmed up and then prefer to be run under load for longevity. Idling, say just charging batteries will cause the cylinders to glaze ....

Anyway, I run my anciente Yanmar flat out all the time and the rev counter still won't go above 3200 rpm! - No smoke but the oil as soon as is changed every 50 hours and at the end of the season goes blacker than black ... instantly.

Hearing about the diesel horror stories, I'm glad that I don't have a Volvo.

 

[oldharry]

Re: Just like m/s car silencers

Diesels thrive on hard work, and the advice to run a diesel hard for half an hour is very sound. Slow running, half speed or less will result in a build of soot and carbon in the combustion chambers, around the rings, valves and injectors and in the manifold. 20 - 30 minutes hard work burns it all off and leaves everything nice and clean. This is why you see all those angling boats roaring home at the end of the day at full throttle. Its not just that they want to get to the pub, but they are blowing through their engines after a day pottering around at low throttle.

Many garages make a tidy profit from thrashing customers diesel cars for half an hour. Our local vicar runs a diesel car which is the bane of the local garaghe mechnaics life. Revd potters around rarely going more than a couple of miles at a time between visits and meetings, and being a good clergyman drives ever so carefully within the speed limits etc. Result? His engine never has to work hard, and is rarely properly warmed up. Around every 2 - 3 months it turns up at the local garage - poor starting, rough running etc: Geoff the mechanic checks the oil and water, then simply takes it down the motorway for half an hour without lifting the bonnet again and returns it to Revd, running sweetly - clearly an answer to prayer!

Oh, and its usual for the oil in a diesel to go black almost immediately. Ideally the engines oil system should be flushed with a cleaning compound before oil/filter change. Adding Wynns oil cleaner to the old oil fifteen minutes before an oil change helps enormously. The fresh oil remains clean for far longer, which must be good for the engine!

 

[vyv_cox]

Oil myths

My Lubricants Marketing colleagues will love you! The only value in flushing engines is to sell more oil. The reason that modern diesel oils go black very quickly is that they have high detergency to ensure that deposits are carried around instead of sinking to form sludges. The carbon that makes the oil black has very low particle size, less than about 10 microns. Anything bigger is taken out by the filter. Small particles do no damage because they are smaller than the bearing clearances.

No lubricant manufacturer supports the addition of any additives like Wynn's, Slick 50, "upper cylinder lubricant" or any other hocus pocus products. Lubricants are a complex blend of additives and adding something else may promote a variety of harmful reactions, but especially sludging. Look at http://www.the-oilman.com/questions/link4.html for some interesting views on this subject, especially the famous test in which vehicles were run with oil drained from their crankcases.

 

[oldharry]

Re: Oil myths

Couldn't agree more about the use - or rather uselessness of long term additives like Slick 50 - whose makers I beleive are facing major court cases in America after their product fouled up several engines and damaged them...

And yes, I very rarely waste time on flushing engines, unless - as low use auxiliary engines often are - they are heavily sludged, and have not been made to work hard.

However, having taken to using Wynns flushing additive as described while waiting for the engine to warm up prior to an oil change, I continue to be surprised how much cleaner the new oil comes up once the engine is back in service.

I know that the particles blackening the oil are small enough to be passed by the filters, and are therefore smaller than the bearing tolerances - but grinding paste is still grinding paste, whatever the particle size! I feel happier (OK - subjective reaction - no scientific basis etc!) to have found a means of removing even more of the muck that is grinding at my engine bearing surfaces in service.

Having said that, it is probably true that the actual long term effect is probably going to be negligible in terms of engine service life! I just like the idea of giving it the best chance - and NOT by running it with additives which modify the complex and carefully constructed chemistrys of modern oil with highly questionable results!

However as I am about to chuck out the old oil, an additive which helps get rid of oil-born particles of whatever size at the same time, seems not a bad idea to me. I would certainly not consider running for any length of time whether on or off load with this or any other stuff in it!

There is no additive that will beat regular oil and filter changes. One taxi driver I know has completed well over a half million miles in his diesel taxi on the original engine simply by changing the oil every 5000 miles - even though the manufacturers recommendation is for longer.

 

[LadyInBed]

Re: Oil types

Does anyone go for the top price or medium price Synthetic oils, or the older cheaper traditional oils – I don’t mean the cheap bottom end products.

 

[chippie]

Re: Oil types

I am starting to think that going to quality synthetic oils is the correct way to go. (mobil 1 etc.)The evidence is compelling.
I will continue to use special additives for specific things (Flushing etc.)

 

[vyv_cox]

Re: Oil types

Use the API ratings. For normally aspirated diesels this means don't go higher than CD and for older engines even a CC would be preferable. My new Yanmar 3GM manual calls for CD. In Shell terms this means Rotella X. The cheaper stuff sold by car parts stores and Halfords is often CD rated and is perfect for yacht engines.

The higher rated oils, like CG and CH, are intended for the much higher temperatures generated in turbo-charged truck engines running flat out across Europe. Shell's Rimula X is excellent stuff for that duty but it has a high base number to cope with increased oxidation rates and higher sulphur fuels. Use of high base number oils in colder-running engines will lead to higher rates of bore wear. Synthetics are intended for even higher temperatures and they have little use in the auxiliary of a yacht.

 

[aztec]

read the above posts with interest, if you're worried about your oil being "black" increase the number of oil changes, so that there is less crap held in suspension..also once the filter is "full" of this crap it will bypass under load. use flush/addatives if it makes you feel better, but iv'e never "seen" any benefits of using it, and i live inside engines. use only oil that is rated for your engine...case in point, one of my customers was told to use fully synthetic oil in his (modified) mazda V6, now with only 46K on the odometer it needs remedial repair work, as the index was not correct for his engine.
the main reason for slow running diesels to glaze is underheating, the top of the engine around the exhaust manifold runs significantly hotter than the rest, causing glazing, working the engine under load allows heat to be spread more evenly throughout the whole combustion chamber which includes the sidewalls of the bores.
Morale of the storey:- clean oil = clean bearings, if you want an engine to work then work the engine.

have a happy crimbo, luv steve XXX

 

[Bergman]

I don't understand how making rest of cylinder hotter allows the bit around exhaust valve to be cooler.

In fact I am totally confused by this thread.

Almost all advice seems to be contradicted by next entry.

Is there a definative line on this.

I think I will try steam, flash boiler - doubles as central heating - 2 cylinder compound engine direct to shaft - modified calorifier as condenser

How about it?

 

[chippie]

Re: diesels re Vyv Cox

Thankyou , I hadnt considered the lower running temperatures. I'll use synthetic on the road and mineral based at sea.
You mention higher sulphur content. Does Britain/Europe sell a different grade of diesel for boats?

 

[adarcy]

Re: diesels - glazing

Dear Aztec/Steve,

Re glazing. INMHO your explanation is incorrect. Ignoring the typos which imply the hot top of the engine "causing glazing" elsewhere, your logic is that the cooler than normal sidewalls cause the deposition and glazing. But surely, the temperature of the insides of the sidewalls don't vary that much as most engines are watercooled somehow and the block is held at its desired temperature. Obviously, I accept that when you hammer a motor the insides get hotter than normal (heat flow etc) but there should not be that much difference at the sidewalls until the whole thing overheats.

I always thought the problem is low engine load = lower turbo boost + lower fuel =I accept lower heat but more importantly = lower bmep and much lower pressure on the rings = aloowing new rings to rattle about a bit and some blowby of combustion products. Therefore you get a polishing effect. If the engine is moderately loaded when young, the rings bed in by micro-scuffing and give a better gas seal. Once that's done, you can do what you like with it but if glazed when young it's very difficult to get the rings to bite on the glaze and form a good seal later. Hence talk about stripdown and a bit of wet'n'dry !

V interested to hear if you think I've got the wrong end of the stick.

Anthony

 

[ccscott49]

Re: diesels - glazing

I'm a diesel engineer and you are completely right! We have a special tool, rather than wet or dry, called funilly enough a "glaze buster".

 

[longjohnsilver]

Re: diesels re Vyv Cox

Sulphur content of marine diesel is currently half or less than that of road fuel in UK.

 

[oldharry]

Re: Changing oil filters

Aztec makesa very important point, which is often missed: when an oil filter clogs up and no longer passes sufficient oil to lubricate the engine, a failsafe bypass valve opens and allows the oil to continue to circulate.

This avoids the immediate and catastrophic failure of the engine through oil starvation - which can occur within 15 seconds of oil supply shut-down. However, it does allow the unfiltered dirty oil from the sump to circulate the engine with an immediate big increase in wear, leading before long to severe damage to the engines bearing surfaces.

 

[johnt]

Re: diesels - glazing

Im just wondering how this part of the thread squares with the Yanmar 2Gm problem.....It has unbalanced coolant flow!

No2 cylinder has no coolant port in the head gasket.. so the water goes in , flows across the bottom, up the centre and around no 1 cylinder, and back out across the cylinder head,

and YES, my engine (about 2000hrs) does show signs of heat stress on No 2 cylinder