How do you stop a runaway diesel?
 

I'm redoing my stop valve, read a few posts, and a few of them were talking about having a chunk of 2x4 ready, just in case they put the new stop valve in wrong and a runaway diesel occured. They were talking about putting the wood over something, some flex tube or something? But they had that prepared ahead of time just in case. What is that something?

In short,

1) It seems like the stop valve would only go in one way, but I guess not.
2) If it's in the wrong way, then you have a runaway diesel.
3) What do I need to do, to prepare for that if it happens?

Thanks,

Jeff 1991 300d, 114k

Not sure about your year, but there are two ways to stop a diesel, starve fuel, as mentioned you may not be able to do that, or starve air. Use any appropriate means.

Take off the u-tube from over the turbo, have a piece of wood near by and have a helper start the engine for you while you stand by the turbo.

Runaway can be a very fast event. When it occurs, it's usually over (engine parts thrown across the shop) before you have time to react.

Starve the runaway of oxygen.....
 

A Halon or carbon dioxide fire extinguisher aimed into the air intake of the air cleaner or just into the air intake next to the radiator will starve it of oxygen. Is a little quicker as you don't have to waste time in pulling off hoses.

Regards

Run-em

Yes, but those are far more expensive than 6" of 2x4 wood and just as fast as the wood if you already have the duct off of the turbo inlet.

With a true run-away, you won't have time to grab the extinguisher or take off any tubes before your rods daylight the block.

HERE is a good video example of a near-runaway engine. Notice how quickly it goes over the RPM limit. They stopped the engine by shutting a flap in the intake.
THIS is an extreme example, but shows exactly how quickly an engine can revv to destruction.

I'd say use your hand
 

Assuming that most of us who do our own service have adequately sized male hands. Even without the "U" tube on it can be done safely, though it wouldn't be nice to stick you finger in the impeller of the turbo. All you have is a high vacuum there, about the same as over a carburator on a fast running gas engine. So with a properly placed palm of the hand over the intake the engine is dead. Do it with the "U" tube attached (with the air cleaner assembly off) makes it even easier and safer. It will leave you with a circle of grease on your hand. Don't let your kids do this, this is only for you.

Yikes! :eek: This MIGHT be safe at idle. Use a 2x4, or a book...

I had a guy tell me about a runaway detroit diesel shooting a rod thru his buddy who was trying to stop it. Plan the approach.

It's safe at any engine speed as long as your hand does not contact moving parts. Vacuum can only pull as hard as the atmosphere can push it, at most it's 14.7psi which is not dangerous with a 2.5" hole.

You go first. :D

I have. Shall I do a demo and post a video for you?

What ever you do, DON'T try to stop it with a rag or any type of cloth or paper as the engine will pull it in and the stop valve will no longer be an issue as the new engine you get will probably have a new on already installed. Words of wisdom. No I didn't do it but I saw it happen on a Peterbuilt. Wasn't perty.

It's a total force of about 70-75 pounds, so you decide. It might leave a mark if you have that force pushing you hand into the sharp edge of the steel intake tube.

Don't use your hand.

I've seen what a partial vacuum can do, skin isn't designed for that. Most larger engines with runaway flaps (DD 92-series for example) have a metal flap on a cable marked "emergency shut down" or other.

I had a runaway 10.4liter Caterpillar, was able to keep it at torque-converter stall speed until I starved it of fuel, which took too long to save an engine unloaded in neutral. Block of wood is best IMO or a metal plate.

If I had the u-tube off .....a tennis ball ?

You know you're talking about a runaway, ... max. RPM or higher, not an idle. Personally I'd rather you don't do a demo, I'd rather say you're right and let you keep your hand.