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Old 07-19-2007, 06:22 PM   #1
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Some years ago in our marina a new motor cruiser was running his engine at the dock. Low and behold - RUNAWAY. After lots of running around & shouting on the dock and no-one knowing what to do it suddenly stopped (after what seemed like a very long time). The result - lots of oil and engine block pieces strewn all over the engine room.

Fortunately, this is not a common occurence but it certainly can happen.

Has anyone here had this happen to them? And, how did you stop the engine? What did you learn from the experience?

Some research on this rather frightening experience:

From a Mercedes website:

General causes of a run away diesel:

If the turbo seal leaks on the intake side, it feeds unregulated fuel into the combustion chamber.

If the piston rings leak on the compression stroke, the crank case oil mist gets blown through the CCV (crank case vent) and into the intake, this feeds unregulated fuel into the combustion chamber, add a restricted or dirty air filter and you have a run away diesel.

An over full crankcase oil level can cause massive unregulated fuel into the combustion chamber leading to a run away diesel.

If the intake valve guides leak and the head oil drains are clogged with sludge, it feeds increasing amounts of unregulated fuel into the combustion chamber, which can cause or contribute to a run away.

If the piston rings leak on the intake stroke, it feeds unregulated fuel into the combustion chamber.

The larger the volume of unregulated fuel going into the combustion chamber, the greater the risk of a run away diesel.

Your best defense against a runaway is:

A clean intake system and air filter.

Regular oil changes.

Keeping a log of oil consumption.

Watching for excess smoke in the exhaust.

How can you stop a run away diesel?

There are three ways I know of to shut down a run away diesel:

Seal the air intake and starve it, this can be impossible if the duct work is on the intake.

Shove a 20 pound HALON or CO2 fire extinguisher in the intake and empty it.

Run for your life and come back when it has stopped naturally.

CAUTION: THE DECOMPRESSION LEVER MUST NOT BE USED TO STOP THE ENGINE EXCEPT IN EMERGENCY SITUATIONS SUCH AS RUNAWAY ENGINE OR THROTTLE DAMAGE, AS SERIOUS DAMAGE CAN BE DONE TO THE EXHAUST VALVES.

************************************************** ******


Shutting off the fuel supply will not necessarily stop the "runaway" as it could still run on the oil at extremely high temperature.

And, from a Yanmar website:

"Hydrocarbon vapors in the intake air will sustain a runaway even with the primary fuel source removed. A diesel engine will burn a very wide variety of fuel, especially when at operating temperature, fuel is fuel, if it burns the engine will run, crank case oil will burn as fuel."

PLEASE share any knowledge of this possible problem.

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Old 07-19-2007, 06:36 PM   #2
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Shut-off the fuel supply and slowly pour a cup of water into the air intake. It will turn to steam as it hits the intake manifold then cool the intake gasses. If you do it too fast, you'll get hydro lock, and that will surely stop the engine. I certainly don't recommend this method, but it could work in a pinch.

The CO2 fire extinguisher is probably the best idea.
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Old 07-19-2007, 07:11 PM   #3
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Slip a piece of plywood over the intake - combustion requires air.

Never attempt to use your hand!

Kirk
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Old 07-19-2007, 07:39 PM   #4
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Quote:
Originally Posted by Gallivanters View Post
Slip a piece of plywood over the intake - combustion requires air.
Or maybe keep a tennis ball in the engine room and hope like hell that access to the air intake is easy when the engine is "screaming".

Phew!
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Old 07-19-2007, 08:56 PM   #5
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Found this:

"Diesel engines will runaway uncontrollably if there is a lubricant or fuel leak into the intake tract. Broken piston rings or failed turbocharger seals can cause a diesel to run at almost full power with no input from the operator."
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Old 07-20-2007, 01:29 AM   #6
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According to Michael, the mechanical engineer:

If you can safely put the engine into gear, thus loading it, the rpm will remain in a much safer range. I had one experience in the Navy on a crash boat where one of the twin Detroit diesels ran away. We slapped it into gear and turned off the fuel supply, which stopped the engine after about 90 seconds. Meanwhile the boat was heading up a narrow waterway with the starboard engine making the boat hard to maneuver. No damage was done to the engine and we found out that the injector pump governor had caused the problem.

In theory, pouring in water will work, but due to the emotional overload of the moment, guessing the proper amount for safe shutdown would be hard to manage. You don't have a lot of trial-and-error time before the engine will be seriously damaged or self-destruct, so the CO2 fire extinguisher discharged directly into the air intake will choke off the combustion air and kill the engine without causing any damage.
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Old 07-20-2007, 04:00 AM   #7
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I am always thankful for the good things I learn here. I am going to buy a CO2 extinguisher which I can mount close to the air intake on the GM353.

Thanks

David.
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Old 07-20-2007, 05:48 AM   #8
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This is exactly why I love reading these boards!

Runaway Diesels!!!!! Who knew?!?!

Now however, I know... and more importantly, I now know what to do about it!

Thanks!
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