How often do diesels "run away"?

[Gale Hawkins]

A several years ago I was the manager for an oil company and one of our delivery drivers was delivering gasoline to a bulk plant, the engine of the truck ran the pump to transfer the fuel, and the fumes from the gasoline were enough to run the diesel in his truck and there was a runaway. The driver was killed. Since that time all the truck engines have been equipped with a flapper system that will completely block off the air supply to the engine.

When in college I dispatched from midnight until 7am for an oil drilling company in Abilene TX and one mud truck had the flapper system in case it got in a low spot filled with natural gas hit in the drilling process.

It was kind of funny how new drivers would kill it by pulling the air shut-off then call for service because it would not start. I never saw it but had one of the guys in the shop had explained the system to me. It always took the guys at the rig by surprise when I would say before I call for service open the hood and on the left side open the emergency kill air intake because pulling it would close the flap but pushing it back in would not open it by design.

On one forum some guy poured Sea Foam into his diesel intake like it was a gas engine. He got lucky per his post because he just bent push rods so he did not have to tear it down.

A run away engine can be a killer as noted. An air kill device can be handy but never say a tractor with one or most any diesel engine.

 

[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.