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Old 08-14-2004, 03:08 PM
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Post Run away diesel, why does it happen?

Run away diesel, why does it happen? Article by whunter

Hello Everyone

Run away diesel:
This is a known problem with diesels, and any diesel engine can have it happen.

What causes it?
The answer is unregulated fuel entering the combustion chamber.

Why is it dangerous?
Because; the normal way you shut down a diesel engine is by stopping the fuel from getting to the combustion chamber.

How can you stop a run away diesel?
There are three ways I know of to shut down a run away diesel:
#1. Seal the air intake and starve it, this can be impossible if the duct work is on the intake.
#2. Shove a 20 pound HALON or CO2 fire extinguisher in the intake and empty it.
#3. Run for your life and come back when it has stopped naturally.
Never use water, it is none compressible and will break pistons and rods; this can puncture the block and throw pieces hard enough to kill you.

Diesel engine cycle theory:
To understand the problem you must understand diesel engine cycle theory; intake stroke, regulated fuel is injected, compression stroke, power stroke, and exhaust stroke vents the cylinder.

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.
Diesels are called oil squeezers because the friction heat of compression causes combustion.
There is no throttle; engine acceleration is controlled by the volume of fuel injected.
A diesel will keep accelerating for as long as increasing volumes of fuel and air enter the combustion chamber, the end result is that it will reach destructive engine speeds that will break things or explosively disassemble your engine.
Even professional diesel mechanics have had diesels run away.

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:
#1. A clean intake system and air filter.
#2. Regular oil changes.
#3. Keeping a log of oil consumption.
#4. Watching for excess smoke in the exhaust.

Here is an odd example that could have wrecked the engine.
Starting problem Help, engine runaway

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Last edited by whunter; 03-06-2013 at 03:19 PM.
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Old 08-14-2004, 07:28 PM
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Your best defense against a runaway is:
#1. A clean intake system and air filter.
#2. Regular oil changes.
#3. Keeping a log of oil consumption.
#4. Watching for excess smoke in the exhaust.
#5 No stinking turbo.
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Old 08-14-2004, 10:22 PM
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block of wood works every time. forget about hands and shop manuals. and like what's been said, CO2 works. Seen a few run away in the army, the
multifuels. It was running on high octane gas at the time, came in overheating (it was 105 F at the time), screwball mechanic took over safety shut off to get at the IP, started it up and away it ran. lucky that Motor Sgt seen it before, had a block of wood and covered the intake. the intake feed
pipe crushed due to the force of the turbo intake, and the metal tube cut a 1/4" groove in the wood block, but it did come to a stop, without wasting the engine or blowing up the motor pool. Loved those Multifuels...NOT.
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Old 08-14-2004, 10:55 PM
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You forgot the main cause in MB diesels -- incorrect installation of governor linkage on R&R of shutoff solenoid or vacuum governor. Not too many other things go "wiffy" on Bosch injection pumps.

I vote for CO2 or loosening injector capnuts for shutoff on an MB diesel. Other engines this won't necessarily work (the CO2 extingisher will, always -- Halon isn't safe, nor widely available anymore). Many engines have unit injectors, so no capnuts (and some are under the valve cover, too!). Electric solenoid cutoffs will almost always shut down when you pull the wire, too.

NEVER put you hand over a turbo intake, SERIOUS injury is likely to occur (loss of hand!). The turbo won't slow down much as it minces your fingers!

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Old 08-14-2004, 10:59 PM
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I saw an engine run away in a 63ft Ocean sportfish. I think it was a 12V92TI or it might have been a 16V92TI. The owner was coming into the harbor at wot, when he went to pull back the throttles the port engine would not come down. Now keep in mind he was a novice boater who had just bought the boat, and he was heading into a crowded harbor at 30+ knots, he was about 1 1/2 miles off the at the time. He also tried the emergency shut off's but they didn't work for some reason. Well insted of turning the boat around and heading back out to figure out the problem. He decides to take it out of gear!!! Now we are talking about a diesel running at 110%, now with no load, my god that thing smoked and made noises diesels shouldn't make! Black smoke was pouring out of the exhuast, the boat looked like it was on fire! I was about 1/2 a mile off it at the time. It seemed like a long time but probably no more than a minute the engine self destructed and went silent. The police etc came out but the Ocean did go in under it's own power. My dads friend is a diesel mechanic, he had just finished majors on this boat the month before. He was called back and basically came to the conclusion the engine was shot, it sucked the turbo in! Rods and valve peices were everywhere he said. What a mess, but nothing $100k couldn't fix. I don't remember what failed a fuel valve of some sort. In hindsight the boat only had a couple hundred gallons of fuel on board he should have pulled the starboard engine back and let the port suck the fuel dry.
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Old 08-15-2004, 12:12 AM
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I was a little paranoid before Larry's mishap
Destroyed the Engine in my Daughter's 300D
Destroyed the Engine in my Daughter's 300D
now I am really a little freaked. the thought of my diesel running away and having to scramble to save it is more than a little disturbing...

What I'm wondering is could I install four cutoff valves? One on each line between the IP an the injectors? Seams like flipping four valves would be a lot quicker and easier than breaking the lines loose with a wrench with it screaming mess to clean up either...

Last edited by whunter; 04-22-2007 at 03:08 AM.
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Old 08-15-2004, 01:48 AM
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Don't waste your time.

If you are really concerned about a runaway.
Go to your local race shop and buy a CO2 remote extinguisher, mount the nozzle into the intake and the switch on the dash.
You ever hear it revving up, hit the button and it dies.
Don't forget to carry a dry chemical extinguisher for other emergency use.
Have a great day.
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Old 08-15-2004, 10:04 AM
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Mr. Hunter

I want to thank you for clarrifying and expounding on this interesting hot topic...

Surprisingly no one mentioned

1.)Leaking fuel injectors...

2.)A faulty cruise control electronics/mechanical faults...

3.)Faulty governor / injector pump / shut off valve...

4.)And of course the proverbial crankcase oil making its way into the combustion chambers... which was expounded on thankfully...

Maybe all the persons who have witnessed/knowledge of a diesel engine running away on "crankcase oil" could be compelled to tell all of posterity about it...

That would be like "icing on the cake" in this thread...

Again thanks and good luck with all future events...
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Old 08-15-2004, 10:20 AM
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Read about a couple of VDubber's on the VW TDI forum who had turbo seal failure, one stopped his by leting out clutch and standing on the brakes & saved engine. One had automatic and the anti diesel valve failed to activate, scratch whole engine. Anti shudder/run on flap was stuck with heavy soot build up, causing engine self destruction.
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Old 08-15-2004, 05:01 PM
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Stop wondering. You could put valves in the injection lines but it would have disasterous results.

Once the measured amount of fuel is in the IP barrels, the IP is a constant flow pump. With the valves you installed closed, the pressure curve of the fuel would go straight up until something exploded.

It would be equivalent to filling your engine with water, keeping all the valves closed and turning the engine with an almost infinite torque. Something would have to give. This situation is called hydrolock. The IP would also be hydrolocked if valves on the IP lines to the injectors were closed.

And where would you get valves that would withstand the 1500 PSI normal pressure in the injection fuel lines?


Last edited by P.E.Haiges; 08-17-2004 at 10:01 AM.
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Old 08-15-2004, 08:02 PM
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Had a 606 run away on me on motor oil. There's a bulletin out about that, about how you're supposed to let the oil spout run towards the front of the valve cover (down the t-chain cavity) instead of back towards the valve seals. If you try to start it too soon, it does something goofy like sucks oil past the intake valve seals. Man, smoke city, couldn't see the other side of the shop. First oil change too. Held together just fine, lasted I dunno, things happen so fast-30 seconds I'd guess?
In school we had a plastic lunch tray from the cafeteria to block airflow if we had a runaway, instructor wrote "The Big Switch" on it with a marker, someone had to use it once in class, no clear recollection of that event. Early 80's, all kind of a fog now.
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Old 08-16-2004, 12:25 AM
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Earlier this year my '80 240D ran away. My son unknowingly overfilled the crankcase with 3-4 quarts more oil than it should have had. The car had smoke prodigously before, but when he cranked it up, it kept going higher and higher. He turned off the key but it kept going. Opened up the hood and couldn't see the shutoff lever through all the smoke. The people in the paint shop he was parked in front of came running out with fire extinguishers and the people across the street called the fire department.

My son commented that he didn't know the engine could rev that high.

I came by 15-30 minutes later and noticed the breather hose was disconnected. Son acknowledged that it came off shortly before the engine stopped and that oil was spraying out of it. That answered the question as to why it ran away and why it stopped.

Engine would only start with ether after that on two cylinders. 3 cylinders after it warmed up. And a big rod knock to boot.

Gave the car to charity. It was sold to someone who is going to rebuild it.
Michael LaFleur

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Old 08-16-2004, 12:40 AM
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Paranoia is setting in.... although I keep my car in tip top shape, it seems on a 20+ year old car anything could happen unexpectedly. Crossing my fingers, and keeping on top of preventative maintenance. I hope I dont have nightmares about it tonite!

Very interesting/informative/important post!

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Old 08-16-2004, 09:12 PM
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Mandatory maintenance is how I look at it.
Survival of the best kept.
Sloppy, lazy or ignored diesel engine maintenance is the biggest culprit.
Untrained people messing with the injection pump cutoff is another.

If you ever replace the injection pump cutoff; take every possible precaution, or ask Larry's advice before you touch it....

Last edited by whunter; 04-22-2007 at 02:49 AM.
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Old 08-16-2004, 09:38 PM
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The incident that MBLafluer mentioned, must be why there is a warning label on most diesels "Do not overfill engine oil, SEVERE engine damage may result." Hmmm.

On another note, may be why most "big rigs" carry a fire extenguisher. (A good idea on any diesel??)


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