Runaway diesel engines

[skipperpete]

In my daily work, I often deal with engines that have either had an overspeed or are in the process of getting to a point where an overspeed is possible. I’m wondering if anyone on the forum has any first hand experience with this damaging event and how it came to pass...... but only first hand info, there are too many urban myths here where a friend or friends friend had a runaway main engine or generator. Some engines are practically immune to this phenomenon, others are very susceptible so I’m interested to hear about your experiences and how you managed the incident, what damage occurred.... and what engine was it.

[Jammer]

First hand, no, but I used to live near an agricultural equipment repair shop. They had runaways rarely but they did occur. Usually a jammed injector pump rack, less often atomized fuel or oil getting into the intake. Management was a shop rag in the intake followed by a CO2 fire extinguisher for last rites. Or just the CO2 if it's handy. When I was working on diesel equipment years ago now I was careful to have a CO2 extinguisher handy, less so now with marine diesels.

[skipperpete]

Good moves, if you can get the oxygen out of the equation the problem is solved. Blocking the intake manifold only partially works if the PCV hose is led to the manifold

[Diamond-Esp]

SkipperPete, Yes I had an incident several years ago whilst sailing from Tasmania to WA (Australia). It happened at about 2am (of course), we tried to get to the air intake but it was at the rear of the engine with a pipe pointing downward. There was no chance of getting access from the front engine hatch without lying on the screaming engine. We tried to access from the rear, but the yacht had completed the Sydney - Hobart race and the lockers providing access were filled with race sails. One of us shut off the diesel in case of injecting diesel into the hot space (so hot that I was worried the fuel lines might melt). Anyway, the engine let out one final squeak before we had silence... It only lasted several minutes (a long time), and the heat was unbelievable, we consoled ourselves by sitting in the cockpit eating a whole packet of Tim Tam's... Not a fun experience... I could provide a lot more detail about what we had done previously, and what I should have done to prevent the problem but in hindsight everything is easy!!

[skipperpete]

Did that happen while she was in gear or running light to charge batteries? That’s a bad stretch of ocean to have an engine failure, especially a destructive one like an overspeed. Can you recall what make of engine it was?

[Diamond-Esp]

Yes we were in gear, but the yacht chewed through battery power so we had to run it every few hours. It was a very well known brand starting with a Y.. I know there were other factors involved that didn't help so. We had been through some less than average weather with a lot of water over the boat, I believe seawater in the fuel was one such problem.

[Cavalier MK2]

Often a timing issue, had that problem in a Volkswagen when the mechanic forgot to set it after a engine swap.

[Briis]

I have first-hand experience since my about-to-be-bought boat almost burned down because of the runaway. Fortunatly I didn't buy that boat then (obviously).

Runaway is very rare, but can happen to most diesel engines under bad very circumstances or coincidences. Particularly more if the engine had long not been used, with valves/sockets corroded, carbon-deposited or oil seals brittle. Turboed engines are the most prone to runaway compared to naturally aspirated diesel engines though. First get's it's oil through turbo/intercooler. It will not stop until it's mechanically seized or burnt out of engine oil (the first scenario is more likely since no engine can take overload revs for very long to burn out multiple liters of engine oil it contains).

Since on a boat you can't manually stop the max-revving engine via last gear and clutch like on (manual gearboxed-) car, truck or tractor. I've seen this many time from my grandpa and his friends with his older soviet-era crap-quality diesel engines that had leaky intake valves - it was a great show of skill from them to manage those situations. Thus the ONLY way to stop a runaway diesel on a boat is to block air intake.

Since I've learned from my past runaway accident, my current (a non-turbo engine, obviously-) I've modded the air cleaner intentionally to come off with managable force in two seconds so I could put my hand or smaller rag on the main air-intake manifold pipe below to kill the engine immediately and effectively via air-starvation. If your's don't have this possibility with your engine - have a correctly sized thick plastic bag prepared that fits over air filter with flexible rope or rubber band in the rear to block all possible air-flow into airbox that you can put over it to succumb the engine via air starvation.

Beware this must be done within 15-30 seconds max to avoid serious engine damage and in most cases and the visibility is way below half-a-meter by that time in the engine room and exponentially your boat soon will be full of smoke anyway from the burning paint, oil-residues etc near exhaust and engine head parts. Hence you must be prepared for VERY quick action to block that air intake in case that rare runaway happens, if you want to be able to save the engine (and possibly your boat as well).

[Ixium]

Some of my countries military light vehicles have turbo’d 2.5L diesels. They are inadequate to move the vehicle when empty, so even more so when you add anything to the back and a generator trailer.

By the books way of dealing with runaways was to cover the air intake snorkel with anything you could get to form a proper seal.

Reality was most times people would shoot fire extinguishers into the air intake and on the engine. Way more of a mess and always a written off engine.

[Briis]

Just to illustrate my previous text on how much smoke and noise there is for those who haven't experienced a runaway diesel yet:

https://youtu.be/fJIcxMJevII?si=fDBlf3gp3DejtCvY

[CrispyCringle]

Crazy amount of smoke in that vid link. Must be from an oil fed runaway.

On a boat, if you are in gear does the prop just cavitate or can you get a 40' sailboat up on plane? j/k

[Briis]

Originally Posted by CrispyCringle

On a boat, if you are in gear does the prop just cavitate or can you get a 40' sailboat up on plane? j/k

Good chance you can get it close to plane. In runaway it'll make around 5-10X the power written on paper. It's almost the NOS of diesels, hence if you have 50 HP engine it can be 500 HP engine in runaway mode. Not sure the prop shaft, gearbox and the supporting bearings can take it though

[Pete7]

As a young soldier walking across the workshop floor one morning, a track vehicle engine on the floor in front of the vehicle ran away. Mechanics could be seen running away, apart from one old hand. He pulled the BCF extinguisher off the vehicle, bashed the ext head against the heavy plate to fire it before tossing into the air intake and casually walking away.

The engine came to a complete stop in about 30 seconds and peace was restored.

[deblen]

Every diesel should come equipped IMHO
https://www.amot.com/en/products/die...ring-database/

[skipperpete]

Good point Len, there’s a lot to be learned from the “deep water horizon “ runaways, an automatic strangler on each engine might have stopped the ignition source but I suspect the blowout gas would have found another. At the time, DP2 vessels were not fitted with air intake valves...... for safety reasons!!!...