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post #41 of 50 Old 05-22-2013
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Re: Runaway diesel

running away means the engine continues to speed up . if you don't stop it , it will fly apart. it is a scary situation .

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post #42 of 50 Old 05-22-2013
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Re: Runaway diesel

So a large eastcoast dragger is coming into a crowed port. The oiler, trying to get a head start on shore leave has removed,cleaned and rinsed (with diesel fuel) the air filters .He re installs.Wow. suddenly engine is way past governed RPM. Take her out of gear and probably disintegrate or do a fancy two step in small places. Excessive RPM can be interesting. My best experience was a friends hot chevy . Carb linkage over centered and pressure plate bounced off the pavement , came back up through the radio , dashboard and windshield into the night.Presence of mind (turn off the key) would have helped.

Last edited by Capt Len; 05-29-2013 at 11:36 PM.
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post #43 of 50 Old 08-15-2013
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Re: Runaway diesel

I don't think anyone mentioned this, but you can use a CO2 fire extinguisher to stop a run away diesel.
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post #44 of 50 Old 08-15-2013
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Re: Runaway diesel

As long as you are not in danger of hitting anything you are better to leave it turning the prop as disengaging will allow the engine to rev higher and faster...

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post #45 of 50 Old 08-15-2013
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Re: Runaway diesel

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Originally Posted by chucklesR View Post
Run away on oil has happened to me once.
I put too much oil in while changing it (boat wasn't level while on the hard), then on my first time out decided to test throttle to max RPM. Frothed it right up. Huge clouds of blue smoke and no throttle control all of a sudden.

The governor doesn't do a thing, it only shuts off/restricts the diesel fuel - so the engine continues to get a full load of 'fuel' from the oil froth.
The fuel shutoff (mechanical and electrical both) does exactly as much good as the governor, none.

Since it's got PLENTY of fuel there and air coming in the engine just does what it is designed to do and runs at full out to use all the fuel coming in, and of course more fuel means higher rpm.

The only way to stop it is to choke air (a rag in the intake) or decompress the engine by tripping the lever on the engine.
You'll need to recognize the condition of run away quick - spinning parts at 4000+ RPM can quickly destroy an engine.

Having had it happen to me just once was enough. I keep a rag zip tied in the the air intake area as well as a zip tie (red) on the decompression lever. It's hard enough to stick your face and hand into a engine compartment with an engine that might be exploding in seconds - doing that and then having to look around for a rag/lever doubly sucks.
if the problem is with the fuel delivery system, as mine seems to have been,maybe, the engine will stop running when all injectors are cracked. my engine is perkins .. they are difficult to cut air.

runaway diesel is also caused by engine using its own lube oil to run and continues to increase rpms until overheat and detonation. this one must cut off air flow or ditch compression so it stops or it will detonate and you can lose boat. this cause is not fixed by cracking injectors, i have been advised.

this is mainly caused by excessive blowby, excessive cylinder wear, ring failure...worn, broken, cracked....
mine so far seems to have been fuel delivery initiated.


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Last edited by zeehag; 08-15-2013 at 11:41 PM.
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post #46 of 50 Old 08-16-2013
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Re: Runaway diesel

I would not use a rag as it can get sucked up and destroyed into the engine. Instead I would use a piece of wood or something hard over the intake.
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post #47 of 50 Old 08-16-2013
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Re: Runaway diesel

We had an old carrydeck crane with a diesel engine that became notorious for not shutting down or overrunning. We installed a ball valve just down stream of the the air filter so we could stop the engine. If your filter housing is threaded to the air intake tube, it would be an easy install, assuming you have room for the valve.
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post #48 of 50 Old 08-16-2013
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Re: Runaway diesel

The two scenarios for engine runaways are

1 Pneumatic governor usually the single pipe. I have seen an old Mercedes boat engine with one of these. If the pipe breaks or the diaphragm fails they will runaway. You can pull the stop control and the engine will stop.

2 Any engine where the crankcase breather feeds into the inlet manifold. If there is any significant frothing of the crankcase oil and it passes through whatever trap is fitted you get a runaway. Pull the stop control and the engine will not stop you have to cut off the air supply.

If I got a runaway and could not get to the air inlet to stuff a rag in I would pull the decompressor if my engine had one. What ever damage would be done would be less than the catastrophic failure you get from a runaway. Worth doing a dry run to find if you need to remove something to block the inlet. Perkins diesels often have a filter that I would need to be removed before applying the rag.

While I have never witnessed a runaway that actually resulted in an engine failure that was catastrophic I have taken the breakdown truck to a Commer 2 stroke that had run away and so had the driver. There were bits everywhere and one of the pistons was embedded in a brick wall many yards away.

Last edited by TQA; 08-16-2013 at 06:15 PM.
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post #49 of 50 Old 08-16-2013
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Re: Runaway diesel

Years ago I had a run away in my Hunter 30 powered with a 12HP Yanmar better suited for rice patties. I over filled the crankcase. Started the engine, things seemed fine and then it started to race even though I pull the fuel lever all the way back

Yeah, I knew what could happen so I quickly put the transmission in gear and let the boat do wide circles until the run away stopped. No damages
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post #50 of 50 Old 08-16-2013
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Re: Runaway diesel

Have used the CO2 fire extinguisher method to kill a runaway. It works, but make sure its CO2 not dry-chem. Just as an aside, here is a vid of a 1930's Rapp Semi-Diesel (2 stroke) running away from an overfilled crankcase.

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