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Old 03-03-2010, 04:56 PM   #1
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Diesel engine runaway

Diesel engine runaway is a condition where the engine consumes its own lubrication oil, running at higher and higher RPM until it over speeds to a point where it destroys itself either due to mechanical failure or engine seizure through lack of lubrication.
I was taught many years ago in school U.S. Army track vehicle mechanic school that a diesel engine can run away when you shut the fuel off, from either a turbo failure where the seal fails and pumps engine oil the air intake. Or might happen from overfilling the crankcase with oil, or from a worn engine as gases can blow past the sides of the pistons and into the crankcase, then carry oil mist from the crankcase into the air intake via the breather. I was taught that the only way to possibly shut the engine down was by cutting off the supply of air.
Has anyone ever had this happen to them, I have never seen it happen myself, as all the diesel engines we used at FMC (Airline Equipment Division or United Defense I worked at both) where new.

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Old 03-03-2010, 05:04 PM   #2
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i think it was more common on the 2 stroke engins.

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Old 03-03-2010, 05:33 PM   #3
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The old Detroit engines had an air shutoff valve for this very reason. I have never heard of A Cummins or Cat doing this.
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Old 03-03-2010, 05:33 PM   #4
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It can happen in the oilfield if a diesel powered truck is driven into a pocket of natural gas. The natural gas is pulled in with the intake air and can result in a runaway engine. These engines are commonly fit with a butterfly shutoff valve in the air intake system that can shut the engine down in the event of a runaway condition.

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Old 03-03-2010, 05:48 PM   #5
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I saw it happen once, but don't know what engine it was. The owner was standing there just watching the black smoke billowing, and listening to the engine screaming. I asked him what happened and he said it was runaway due to turbo seal failure. When I asked what could he do about it, he said wait for it to seize up.
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Old 03-03-2010, 07:38 PM   #6
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Diesel engines can operate on hydrocarbon fumes, and since there is no throttle plate, a runaway is possible. Propane , methane, and gasoline fumes could cause the diesel engine to runaway. Turning off the key would have no effect.
Other than a severe propane leak, in a Mh, driving into a gasoline spill at a service station could possibly provide enough fumes to affect the diesel engine...
The solution is to stuff a rag or discharge a fire extinguisher into the intake. (How fast can you climb up to your roof intake with the engine screaming?) Or... drive clear or stand clear until......
I think runaway engines are rare and that same intake on the roof would be less likely to grab enough fumes.
Work Engines at refineries still have air intake shutoff valves..
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Old 03-03-2010, 08:15 PM   #7
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Yes, it has happened to me - a few years ago I had a VW Golf with a non turbo diesel that had about 300K on the odometer. I was on the freeway and the car was going faster than it should have been. I turned off the key and the engine continued to pull. I put it in neutral and coasted over to the side and put my palm over the intake and the engine stopped. It happened slow enough that I had time to think. I had to wait for it to cool before it would run normal. It would do it again as soon as it got hot again. I added a second breather to the valve cover and a condensate 'coffee can' and it was all better until a Buick made a mess of it.

Since then, I have learned to carry a CO2 fire extinguisher and, in the case of my Dodge Cummins, discharge 'into' the curb headlight (intake is behind it) to shut down the engine. I tried it, it works.

Today, I carry a larger CO2 unit in the coach and the air intake is just about eye level. I am mentally prepared.

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Old 03-03-2010, 09:08 PM   #8
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Had a Detroit runaway on the dyno in college. we tripped the air intake shutoff and it just kept sucking air around the seals, we finally pinched the fuel line with vise grips then ran out the door hoping that it didn't gernade before it stopped. It finally died from lack of diesel. This happened while we (I) were setting the "rack". Have seen it several times in the oilfield where the engine got a wiff of "well gas". Ever heard a Detroit V-12 turning about 7000 rpm's? It's a screamer!!

On a separate incident we had a guy walk by a 3 cylinder Detroit with a side mounted blower and it sucked the "red" rag out of his pocket. It's amazing how fast stuff goes through an engine. We were cleaning rag fragments out of the shop for a week. No engine damage was done.

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Old 03-05-2010, 07:27 AM   #9
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My son,who had a turbo VW was involved in a service proceedure with the engine running when he "got rough" with an air conditioning line that was adjacent to the air intake.The line cracked and the engine took off and literally screamed until the R12 was gone.The only damage was a seized power steering pump and they continued to drive the car until it rotted away.
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Old 03-05-2010, 07:46 AM   #10
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When I was in the Navy, one of my duty stations was to run the boiler repair shop on a repair ship, the USS Ajax, AR-6. I took teams to different ships on the waterfront to clean and repair boilers. One night, when I had a team cleaning tubes using a diesel powered high pressure water jet machine (6 cylinder turbo Detroit diesel), the petty officer I had in charge of the midnite shift told me the next morning we couldn't continue because the machine sucked in a valve. I asked him why, and he said it started to run away, so he tripped the emerg shut-off that blocks the intake. I didn't personally witness it, I felt he wanted to get out of work, but that didn't work, I borrowed another one from the base and we finished the job.
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Old 03-05-2010, 08:25 AM   #11
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Seen once, seen the aftermath twice. Had an apprentice try to go an induction cleaning on a Duramax. It finally bent the valves and quit running.

A guy tried to change his own fuel filter on a Duramax and started it with ether. Said it was a warranty item because when he turned the key off it just kept revving. That one knocked two pistons out.

The last one was a Cummins and was the more traditional variety. The return spring inside the pump broke allowing it to run away, by the time they cut the fuel supply line it had puked the seal in the turbo and was running on it's own oil. It pushed the head gasket out and shut itself down without consuming itself.
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Old 03-05-2010, 08:49 AM   #12
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Had it happen in a '79 Volkswagon Rabbit Diesel. The rings were about gone and it was blowing oil into the intake manifold via the PCV valve. It pooled in the intake until it reached some holes in the intake runners. From there it ran away. Strangest feeling to feel the car accelerate without input from the driver. I got to about 65 mph before I figured out that I could just apply the brakes. At 45 HP, the brakes would easily overcome the engine. No damage. A red rag out of the "trunk" soaked up the remaining oil in the intake...
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Old 03-05-2010, 11:37 AM   #13
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I had a V-8 Detroit (318 HP) run away back in the 70's in a GMC road tractor. Pulled the air shut down and the ball fell down the throat and shut it down. Re-set the ball and re-started. I wound it before I could get it stopped and a piston came through the side of the block.
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Old 03-05-2010, 06:34 PM   #14
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I had a turbo diesel Peugeot run away but it was due to the accelerator pump. It was a five speed, I put it in 5th, turned the key off and pushed really hard on the brakes till it stalled out. Pretty scary stuff.

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