How often do diesels "run away"?

[ArmyPair2]

This has nothing to do with tractors but in the old days when I was in the Army we had diesel tanks and there was one tank that would start up on it's own. We all used to call it the ghost tank.

 

[Guesseral]

Man this is my first diesel engine of any kind, and I had no idea what you guys were talking about at first but now that I am starting to understand I am getting kind of worried! Thanks a lot for the extra gray hair its not like I have that much hair left anyways, but still it really is a good idea to know that its a possibility!

 

[Egon]

Man this is my first diesel engine of any kind, and I had no idea what you guys were talking about at first but now that I am starting to understand I am getting kind of worried! Thanks a lot for the extra gray hair its not like I have that much hair left anyways, but still it really is a good idea to know that its a possibility!

Don't worry. All will be well unless you drive into a gas cloud and is highly unlikely. And if that happens chances are good you will not have to worry.

 

[Dave M7040]

I worked in a government department which investigated significant motor vehicle accidents or incidents.
Fuel delivery trucks were prone to the run-a-way experience when dumping their loads at gas stations because to the large gasoline vapor cloud coming out of the underground tank hatch.
I agree with an earlier poster that CO2 fire extinguishers were the fastest way if their was no air shut off valve.
Dave M7040

 

[Wayne64SS]

Any diesel is at risk for runaway, especially any turbo diesel. I have a 02 VW tdi wagon I bought that blew a turbo and ran away on crank case oil, I got it to fix it. There are ways to prevent it, common sense mostly. IE when I blew a turbo I knew exactly what it was. As soon as you hear it pop and see a little smoke and lose power you should shut it off right away. Do not try to drive it. What happens is the turbo comes apart and the lubricating oil pumped to the turbo is then free to enter the intake unrestricted. Diesels run on oil. It's not something you need to worry about. In some cases there isn't much you can do, like that poor guy that rolled his tractor and it run away. No way to shut 'er down especially if HST, it aint like you can stall it.

Detroits are their own breed. Fuel injectors are actuated by a mechanical rotating rack that pushes on plungers in the injector to go from no fuel to full fuel. When a Detroit shuts down the rack springs to full fuel to make it easier to start, then when it normally starts the governor takes over and pulls it back to no fuel. What often happens is (like in the case of that old truck video posted) after it sits a long time the injector gets stuck in that full fuel position. When the beast is brought back to life the governor cannot pull the rack out of full fuel. In the late 70s Detroit updated the rack design to include springs, so if an injector sticks it won't keep the entire fuel rack at full fuel. When they updated them the did away with the emergency shutdown flap, except in oil field and fire apparatus where fuel vapors in the air are always a concern.

A Detroit Diesel doesn't run-away, it over-speeds, the operator runs away. LOL

 

[dfkrug]

Any diesel is at risk for runaway, especially any turbo diesel.

Yeah, since so many diesels are turbo-ed, an old and tired turbocharger can be a concern. Note
that this can also be a concern with engine fires. A turbo gets hot enough to flash oil into flame.
It seems that old and tired turbocharged construction equipment have more than their share of
engine fires.

 

[BigBoyinMS]

I remember as a teenager working in a marine dealership. The shop mechanic told a gas engine could diesel and overspeed as well. I guessing same way, aspirate fuel?

When you say "diesel" in regards to a gasoline engine that's where a piece of carbon buildup is overheated in the combustion chamber and is hot enough to ignite the fuel vapor when you turn the ignition off which keeps the engine trying to run. It won't run away but it still isn't good for it. And aspirating fuel would actually tend to stop it since gasoline engines will only run on a narrow air/fuel ratio and it has to be in a vapor.

A gas engine has two things keeping it from running away or over revving on it's own... the ignition system; turn it off and it stops. And the butterfly(s) in the carb base or throttle body that are spring loaded to automatically be closed which means no (or very little) air for combustion.

The Perkins gas engine in my Massey used to have a bad habit of "running on" or dieseling when I went to shut it down. The carb has an "anti-diesel" solenoid that is supposed to shut off the fuel when the ignition is turned off but it burned out and a previous owner had clipped the tip off so the tractor would run. I used to have to pull the choke when I killed it to shut off the air. I started treating all of my gasoline with Seafoam and now I can kill it by just turning off the key. The Seafoam cleaned all the carbon out of the combustion chamber so no more hot spots.

 

[brain55]

I have been a tractor mechanic for over 25 years and have only had an engine runaway twice, both times were from not getting the pin on the fuel rack lined up properly in the governor arm jamming the rack wide open. Three times if you count the Cat engine on the diesel pad at trade school that would continue to run on its own oil after it was shut off. I try to always be aware of how I'm going to block the airflow if I've made a repair where I could have created a runaway situation.

Brian

 

[Ilikeurtractor]

...And aspirating fuel would actually tend to stop it since gasoline engines will only run on a narrow air/fuel ratio and it has to be in a vapor...

I know this is off-topic, but this reminds me of a question I've had about running diesels on gasoline - will they? In theory, they should not - at least at idle speeds - since the air/fuel ratio is too high. However, I suppose when the injector injects gasoline into the cylinder there is a "flame front" for my lack of better terminology that has the correct ratio and will burn and cause the engine to run. I acquired a tractor a while back which I suspect had gasoline in the tank, or at least a high concentration of it. It seemed to run fine for about 20 mins at which point the pump appartently got hot enough from the engine heat to "vapor lock" causing it to die. Waiting about 10 mins or so and it would fire back up and run again until hot. I dumped the fuel and filled with no. 2 diesel and the problem went away. I noticed the spilled fuel would dry quickly like gasoline when I emptied it.

 

[TnAndy]

I had an 8hp Lombardini diesel on my garden tiller run away once. Cranked it up for the first time one spring, didn't check the oil as I'd changed oil before I put it away in the fall, got about 50' down the drive toward the garden and the engine took off and sounded like a chainsaw at high rev. I had no idea a diesel could even turn that kind of RPM, much less why it was doing it. I jerked the fuel line off....no effect.

What I later determined was tank fuel ( there is no manual shutoff in the line ) must have slipped by a seal in the injector pump over the winter, and seeped into the crankcase. Had I pulled the dipstick and checked, I'm certain I would have found a high reading on the stick. I believe the excess, diluted crankcase oil was sliding by the rings, and firing in the combustion chamber once it warmed up a bit.

SO, it screamed like a banshee for 3-4 minutes, and after pulling the fuel line with no effect, I just backed off and waited for something to fly apart. Nothing did, it finally quit, I changed oil again, and have run it for a couple years now.

Knowing what the deal was now, I'd have dropped the oil bath filter off, and stuff my shirt in the intake....but at the time, I too had never heard the term "run away diesel".

Live and Learn.

 

[BigBoyinMS]

I know this is off-topic, but this reminds me of a question I've had about running diesels on gasoline - will they? In theory, they should not - at least at idle speeds - since the air/fuel ratio is too high. However, I suppose when the injector injects gasoline into the cylinder there is a "flame front" for my lack of better terminology that has the correct ratio and will burn and cause the engine to run. I acquired a tractor a while back which I suspect had gasoline in the tank, or at least a high concentration of it. It seemed to run fine for about 20 mins at which point the pump appartently got hot enough from the engine heat to "vapor lock" causing it to die. Waiting about 10 mins or so and it would fire back up and run again until hot. I dumped the fuel and filled with no. 2 diesel and the problem went away. I noticed the spilled fuel would dry quickly like gasoline when I emptied it.

A small amount of gasoline (say up to 10%) won't usually be a problem. But higher concentrations can do damage.
Gasoline is rated as to how resistant it is to compression ignition.(The Octane number)
Diesel is rated as to how well it will compression ignite. (The Cetane number)
Pure gasoline shouldn't normally ignite in a diesel engine but a high concentration can be ignited by the diesel it's mixed with after the diesel ignites. The problem is that gasoline will ignite at a different time and burn at a different rate which causes "knock" and can actually damage the engine.
Just a guess, but yours was probably mostly diesel but a bit more than 10%.

 

[Ilikeurtractor]

Interesting article on a engine being developed by Chrysler that runs gasoline in a diesel cycle:

Biodiesel Magazine | biodieselmagazine.com

Seems like a lot of problems with running gasoline in a diesel are it can cause problems with the injector pump and components as they rely on the fluid for lubrication. The older Bosch style pumps either use engine oil or thier own oil supply and therefore are a little more tolerant of what one runs through them. In any event, I don't plan on running gasoline in any diesel engine, but am curious as to the probability of it causing damage.

 

[psj12]

The old Army duce and a halfs had a multifuel diesel in them that would burn darn near anything flammable, however gasoline required the addition of oil to help it lubricate the injection pump. Gasoline was considered an emergency fuel only for that engine.