Runaway Diesel - Breather Recirc

[DaveM]

I was reading tech notes in Aug. Mainsheet and saw the article on runaway diesel engines caused by recirculating the oil breather hose to the air intake.  I noted that they were talking about large industral diesels.  Given that new engines come with the recirc system in place I am wondering if this is really a concern on small engines.  Second if an engine does runaway do you have time to stick a plug into the intake or wrap plastic around the intake to shut it down.  Thanks
Goodwinds
DaveM

[Ron Hill]

Dave : My first thought on stopping a "run-a-way diesel" in a C34 would be cut off the fuel! 
I'd remove the steps and see if the fuel cutoff cable had slipped and if it would cut off manually.  If not then I'd put a clamp on the fuel line between the engine fuel filter and the injection pump !! 
A few thoughts

[DaveM]

Ron, thanks for reply. The Mainsheet article makes the point that if on a large industrial diesel the breather recirc is feeding enough oil into the intake it will fuel the engine alone so a fuel shutoff won't have an effect, only cutting off the intake air would stop the runaway. They apparently have something called an airbox (closing flap) that can be triggered to shut off the air. That opinion is what started me thinking therefore the question.
Goodwinds,
DaveM

[Ron Hill]

David : The article is correct - that with the oil pan breather connected into the intake manifold, you can not "oily air starve" a diesel by just removing the air cleaner/noise suppressor and capping off that single intake under the air cleaner.

However, the thought of cutting off the air supply to kill a diesel would definitely be my last choice.  I'd cut off the fuel supply first.    

[Indian Falls]

You have a serious problem if you have enough oil coming out the crankcase breather to run the engine.
The smoke you see coming out of this hose should be blowby which is combusted fuel already.

[mainesail]

Run-away-diesels more often happen on worn engines when crank case oil blows by the rings. Perhaps the most common cause is a blown turbo seal but I don't know of a C-34 with a turbo diesel. I was on a large power yacht when this happened and shutting off the fuel supply does squat. It was far to dangerous to send a man into the engine room so we kept it under load till it burned out.

It can also happen when an older type mechanical fuel pump membrane leaks and thins the crank case oil. You can shut off the fuel but until the engine runs low or out of crankcase oil the motor will not stop. To stop them you need to cut off air.. If you've never been up close and personal with a run away diesel I don't advise it. Pretty scary event...

Run away diesels are quite rare on small Kubota's, in fact, I don't ever recall hearing of one. I have seen one run backwards though, also not pretty..

[MarkT]

The only way I can see a diesel running away is if the bearings on the turbocharger fail in such a way as the engine oil can be fed into the intake. (I know this can happen with Detroit diesels) Seeing as we don't have a turbocharger I don't see where this could happen with our little engines.

[Stephen Butler]

I have been present at 2 run-away situations, both involving larger turbo-charged land based units.  In both cases the fuel shut-off was used, but without effect.  Both engines ultimately ran to destruction, with all staff removed from the area.  No effort was made to block the air intakes as this would have required staff getting close to the units and throwing a canvas shroud correctly....too risky.  It is hard to imagine a small Kubota engine, without a turbo and no previous indication of problems, having this problem.  Having said this, IF our own engine was in a run-away sitution and the engine stop did not function, we would not go below until the engine had stopped on its own.  removing the engine cover to get to the air intake would not be our decision.  Just some thoughts.

[lucky]

Having mechanic for caterpillar dealers for 40 years,I don,t believe a runaway a will happen from a vent line going into the intake.If you had that much blow by the engine would be hard to  start.Runaways are caused  by a malfuction such as govenors weights coming apart,rack limiters not working properly.I've seen older engines runaway, but not newer models.we always keep service manuals handy to put over intake on start up of repaired fuel system,any thing such as rags,or plastic may be sucked in and spit out the exhaust.This is true of large or small diesels,if you feel you must try to stop it by covering the intake,approach the engine from the front or rear,if it comes apart it will throw the rods out the sides or will just lock down when it runs out of oil and there is nothing else to to run on.
Al Landry
hull13
1986 c34

[Terry Forshier]

Some 20 years ago I had this happen to me. I was in my Little ODay 30 with a 2QM15 diesel and was coming back to Naples from Key West on a yes, dark and stormy night in December. I was trying to get the boat home for Christmas as I had been In KeyWest over Thanksgiving but did not have a decent window to get it back that week. I left it in Key West for a month , went back to then home, up North, then back down before Christmas to bring it back for the Holidays to Naples.
I had on board by son in law a automobile mechanic and his brother. WE left a about noon and headed North but the weather kept worsening with winds shifting from the North. We were motor sailing to keep a point across Florida Bay. At about 1 am the diesel just took off.  I had no idea what was happening as we shut fuel off but the motor kept gaining and gaining faster and faster. Fortunatly my Son In Law knew. He took off the cover and on top of the motor were the valve adjustment links (I think that is what they were) He slammed them shut and the motor quit. He diagnosed after awhile that the oil pump seal had indeed broken and the oil was mixing into the cylinders causing the runaway. So at that time of night, with dc lilghts, on the floor, in 3 tyo 5 with about 15 to 20  winds on the nose,we drained the oil tank. Used what oil we had left to refill the engine as best we could. He did some type patch work on the seal and Then we started up and ran under low power motorsailing in. The next day he ordered a new fuel pump and seal. the motor was not damaged and ran great for another 10 years until I sold the boat.
If I was alson on the boat or with someone else not knowing I am sure the engine would have run until it exploded.
A memorable night. Alls well that ends well. .

[DaveM]

Terry
Thanks for the story. Do you think it was the decompression lever he pulled?  I did some further searching and on the Marine Diesel site that pulling the decompression lever is the way to stop a runaway. Of course may cause some valve damage. With the other experiental input a remote on the decompression lever makes sense. Thanks for the stories. I suspiconed that just the breather is not enough on a small engine. However, to keep an eye on the amount of oil on the breather recirc I am putting a Jegs air/oil separator kit as suggested on this site or another.

All this just confirms to me that the article on Main Sheet (August) was a bit over stated on our small engines but worth accounting for with some kind of tracking.

Goodwinds
DaveM

[Terry Forshier]

As I recall the top of the engine had elongated triangles that pivotes on a horizonal axis that were linked together and moved forward and backward with the acceleration or slowing of the motor. He  put his hand on the front one and pushed them back shut. The engine stopped dead.