If always known about runaway diesel engines. And always been paranoid of it. How common is it for a 7.3 idi turbo engine to Runaway?

 

Theres a video of one on youtube, but never heard of nor seen it otherwise.

 

25 seconds https://www.bing.com/videos/search?q...B8&FORM=VRDGAR

IDI's are so classy they try to be stylish even when theyre tryin to blow up.

 

It was common on Detroit 2 strokes especially after rack adjustment

 

A little late, but trying to think about runaway here:
1. The way the IP is designed, the FSS, when released(key off) physically shoves the metering valve side of the governor to full shut off. So, even if the flyweights broke or something, the key would shut it off.

2. Turbo wise, I'm not sure quite how much oil would be needed to keep the motor running into runaway condition, but I suspect it would have to be a considerable amount. You'd need to have the oil seal absolutely destroy itself on the intake side, and even then, I'm still not sure - looking at all the turbos I've seen, the seal is "behind" the compressor wheel - on the high pressure side of it, so as the turbo spins up, it would tend to push oil away from the intake, back through the seal and down into the turbo drain.

3. About the only possible source for oil that I can think of is through the CDR system, though you'd have to create enough of a negative pressure on your air cleaner to suck crankcase gasses, without reducing the inlet air enough to drastically reduce the total HP and have the engine die from lack of air.

Basically... It's really, /really/ hard to make an IDI runaway, beyond the governor. Except for when you mis-assemble the IP top, but even then I'm not sure whether it 'runs away' or simply goes to governed maximum.

 

Ive thought about it as well. IMO there really is no way for it to runaway via the CDR, there isnt enough liquid oil present for the engine to run regardless of scenario (not counting with a turbo).

With turbo however, it really doesnt take that much. Think about how much fuel squirts when you crack a line on an injector, it aint much. Oil seal could do this easily, and afaik, thats the most common cause.

Im sure you know, but by definition, it isnt a runaway if you can turn the key off and stop the engine.

Would love to know how / why the 6.9 in the vid ranaway.

 

See, I was thinking about that, and thinking about my turbo:
Looking at it, pressurized oil comes into the top, and is fed down into the bearing somehow. It drains out of that bearing(at the sides, I'd guess) and into the (wide open) drain port at the bottom.

So, /after/ it comes out of the bearing, it's under effectively zero pressure - because there's no restriction there.

Now, somewhere along the shaft, you have an oil seal on both sides, keeping exhaust and intake gasses out of the oil/drain area... But, if you look at where those seals *must* be, they are "behind" the two wheels.

On the intake side, you only have "vacuum" on the inlet side of the compressor, which is right at the end of the shaft.
Everywhere else in the compressor side must be under pressure(boost - except perhaps at idle where the turbine hasn't spooled at all)
On the exhaust side, you have neutral to positive pressure everywhere.

So, I don't really see how, at least on the turbos I've seen, a leaky oil seal would result in a runaway condition - even worst case, where the engine is idling and therefor has no boost pressure pushing against the seal, forcing it shut. In that case, yeah, you might get some oil getting sucked into the intake... but as soon as the engine started burning it and increasing RPM, that would increase the drive pressure on the turbo, spool it up and create boost that would then push against the leaky seal.

Any thoughts?




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Edit:
Also, one person on another thread here pointed out a good way to make a runaway - spray hot oil right across the CDR intake port(aka return a bunch of oil to the oil filler cap, while having the CDR pull from the IP timing cover at the front, right below it).
Then, you get the turbo spinning hard enough to start creating a vacuum, pulling a bunch of oil-heavy blowby into the engine and there you go.

 

if i remember correctly that pulling truck ran away after something in the injector pump broke.

i have seen it a few times on Mack engines, where the injector pump drive would break. the engine would run away and could only be shut off by shutting off the air intake, disconnecting the fuel supply, or letting it blow up.
one i was able to close off the intake, one by removing the fuel line at the tank, but a Superliner had an under hood air filter and i had no tools to shut off fuel. and there was no way i was opening the hood on an engine that was spinning over 3,800RPM and standing next to it to cap off the intake.
it only took 5 minutes for that one to lockup.