Exploding diesel engine

ZuidWester

ZuidWester

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My BMC 1.5 diesel onboard has been a trusty companion for many years now.

Unfortunately my many years of cruising couldn't prepare me for what happened last week. I was happily chugging up a quiet river alone when the engine started making a ticking sound, which made me immediately throttle down into neutral. The engine then started racing faster and faster and nothing I could do would stop it. The kill button (electro-magnetic actuator) dod nothing and when I opened the hatch the engine looked like to was about to explode: Smoke, stream and black gunk was streaming out to the extent that I dropped the hatch and ran to the bow in panic.

By the time I'd dropped the anchor the engine was dead. Steam and acrid, choking smoke prevented me from getting near the very hot engine. I'd never experienced an engine race like that and there was no way I was going to try starting it again. The only hope was to tow her back to harbour with my dinghy.

Since then I've talked to a mechanic friend who has provided some tips as to how to diagnose the damage: first try to rotate the engine slowly by hand to see if anything internal prevents it from doing so. If so the engine is dead. If not check the valves and pushrods for proper function and then proceed to the injector system to see if the fuel regulator is defective.

After this dramatic scene occurred I was convinced that was it for my engine and the thought of replacing it was daunting. Now at least I can think about going back to the boat and finding out just how much damage has been sustained. The cause is likely to have resulted from uncontrolled fuel input, but at the time I found myself unprepared for this disaster. Physically smothering the air intake would have been advisable, and in retrospect a squirt with a fire extinguisher may well have stalled the engine.

In retrospect we are all wiser. Has anyone experienced anything like this?
 
I knew someone now dead who worked in the engineering department of a large industrial diesel engine manufacturer. They had a massive engine run away under test and the top of the engine blew a hole in the factory roof scattering engine parts for miles.
 
I've heard of this, but fortunately never experienced it.

The air intake on the current boat is reasonably accessible for blocking, but on the new one it's somewhat harder to reach. Perhaps I should stow something nearby to block it with if ever needed; it's a round plastic pipe and perhaps a tennis ball would fit nicely without being sucked in.

Pete
 
Hi Spyro,

Thanks for the link. I suspect the engine in fact did suffer from runaway due to oil mist:

"In many vehicles, a crankcase breather pipe feeds into the air intake to vent the crankcase; on a highly worn engine, gases can blow past the sides of the pistons and into the crankcase, then carry oil mist from the crankcase into the air intake via the breather. A diesel engine will run on this oil mist, since engine oil has the same energy content as diesel fuel, and so the engine revolutions increase as this extra "fuel" is taken in. As a result of increased revolutions, more oil mist is forced out of the crankcase and into the engine, and a vicious cycle is created. The engine reaches a point where it is generating enough oil mist from its own crankcase oil that shutting off the fuel supply will not stop it and it will run faster and faster until it is destroyed."

I just hope the engine isn't dead. I'll go and check tomorrow and let the forum know.
 
Hi sailorman,

Yep, that Land Rover smoked in a similar way. I noticed that the cameraman was hiding behind another vehicle! Scary stuff. A fire extinguisher is indeed useful in such cases as the link Spyro provided also states:

"Several ways to stop a runaway diesel engine are to block off the air intake, either physically using a cover or plug, or alternatively by directing a CO2 fire extinguisher into the air intake to smother the engine."

Something for the future...
 
Do you have gas on board? If there is a gas leak a diesel engine will run away.
There was an accident on the St Andrews fish dock in Hull when a compressor working in an underpass ran away when a leaking liquid gas tanker had to stop in the tunnel.
I seem to remember someone was killed and a few injured.
 
Well, there was a good reason for it and you'll need to find it, but would not trust an engine that's done that to be sound afterwards. Likely to be chronically over revved.
 
Hi Lakesailor,

No gas on board, at least not in the engine bay. I think the diagnosis of a runaway engine running on its own oil is correct. I first heard a tapping sound, which might well have been something breaking which allowed oil mist to enter the cylinders. The kill button then did nothing because stopping the diesel would have not prevented it from running on oil mist.

It's likely the engine is now in need of replacing, which is sad, but not the end of the world. I will keep the forum informed of the diagnosis/pathologist's report.
 
sailorman said:
they will some times pick up sump oil & run uncontrollably on that.
Click to expand...

The chances of runaway are increased if there has been fuel dilution of the engine oil from leaky lift pumps and HP fuel pumps or common rails in modern engines.

Do not be tempted to stop the engine by putting your hand on the air inlet.!!!!

This is an everpresent danger with diesels on oil rigs and they are all fitted with a valve device( Rigsaver) which shuts off the inlet air and can be actuated by overspeed and or the gas sensor system.
 
Hi Lakesailor,

There's no gas on board, at least not near the engine bay. The likely culprit is oil mist causing a runaway engine as Sailorman suggested. I first heard a knocking in the engine, which could have been something breaking, which allowed the oil mist to get through to the cylinders. The kill button would then have been no use.

The question now is whether the engine is salvageable. I will keep the forum informed.
 
The knocking is likely to have been the motor first getting off on the lube oil as it is not a controlled burn.

High oil levels for whatever reason in the sump are the usual culprit in an unblown motor.

Grey / white smoke and copious amounts of it from the exhaust are a good indicator of lube oil runaway. I have seen one or two get away myself. Ford Dover and some small Mercs were a devil for it.
 
ZuidWester said:
The question now is whether the engine is salvageable. I will keep the forum informed.
Click to expand...

Doubtful. At best you have an engine which is worn and letting lots of oil past the rings and into the combustion chambers. At worst, it has revved itself to death because the governor, which normally stops a diesel from over revving would have no effect if the engine was burning its own lube oil. In either case, an engine that old isnt worth investing much money into a repair.

On the plus side there is likely to be a similar engine in useable nick somewhere going pretty cheap. So keep your eyes open for a replace as the lowest cost way forwards.

Your post suggests you have few engine repair skills yourself . So you can look at this as a learning exercise and try to replace the engine yourself. Its easier than you think - they are simple machines that anyone can understand if they take things carefully and slowly. But dont spend lots of money on hiring mechanics to strip down and inspect and report back to you that the current engine is now junk.
 
Might be a 'goner'

ZuidWester said:
Hi Lakesailor,

There's no gas on board, at least not near the engine bay. The likely culprit is oil mist causing a runaway engine as Sailorman suggested. I first heard a knocking in the engine, which could have been something breaking, which allowed the oil mist to get through to the cylinders. The kill button would then have been no use.

The question now is whether the engine is salvageable. I will keep the forum informed.
Click to expand...

I fear that the reason the engine stopped is that one or more of the conrods have bent or broken and that you may have a damaged block so I would be prepared for the worst and as somone else said, you could not trust the engine again.

Trying to be more positive, in the event of the engine being beyond repair there is a company who can supply rebuilt units. The prices are for an outright sale with no engine handed in as I suspect yours will be scrap but worth talking to them. You could then fit all of your marine parts onto the engine.

http://www.pbmechanical.co.uk/engines/index_bmc.htm

Half engine £1,320.00 +VAT

Three quarter engine £1,980.00 +VAT

Full engine £2475.00 +VAT

Alterantive is about £6000 plus all the cost in installing a new engine etc, new propellor and so on. Guess,~ +£2K or more depending on what you do yourself.

PS They also do a full engine (Keel cooled) for about £3500 and that includes a new gearbox
 
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Thanks Bilgediver, It may well be the oil level has increased slightly over time. I thought it was just my imagination, but now that makes sense. I will check this, although I'm not sure how though.

I agree with you about keeping your hands clear of the air intake. I will place a CO2 extinguisher in the cockpit from now on for such incidents. My dry powder extinguisher would probably have left the engine is a right mess.
 
Thanks for the info Jcorstophine,

I reckon investing in a completely new power unit makes the most sense in the medium/long term, although £3,500 is a substantial unexpected investment.

The sooner I get working on this the better. All this happened on the last cruise of the year before she gets put in mothballs for the winter. Who'd have thought that would happen. Next year I intend on going on a long cruise with the new engine to make the most of this disaster.
 
I hae me doots whether a CO2 extinguisher would last long enough to stop a runaway, physically stifling the airflow is probably the best way, a rag/ dishcloth stuffed over/up the air intake (it'll get partially sucked in which will help)or even a sheet of cardboard or anything else you can hold over the intake until it stops. I also suspect that a powder extinguisher would not work, but it probably would wreck the engine internally.

There are several videos of runaway diesels on youtube and though the noise and smoke looks very alarming I'm not sure its particularly hazardous being close to one. It isn't going to explode after all.

Anyway, it's a very rare occurrence so the chances of it happening to you again is all but zero.
 
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