Out of Control Yanmar

Skipper5370 · May 24, 2010

Runaway Diesel

Sounds like a runaway diesel where oil is leaking into the cylinder and the engine is burning the oil as fuel. The only way to stop this is to release the compression via the compression levers usually at the top of the engine.

Texas Lake Sailor · May 24, 2010

What you had was a "run away" diesel. When either oil gets past the rings or you have a build up of fuel the engine starts running on this excess fuel /oil. The only way to shut it down is to use up the "fuel", deprive it of air, (you can if you have one try discharging a CO2 ext in the air intake). Check you fuel supply, your excess fuel return lines and then cyc rings.

KD3PC · May 24, 2010

run away diesel...somehow it is sucking crankcase or fuel oil, and using it as fuel...somewhere you have a leaky injector pump or some such....the only way to shut it off is to choke off the air....with a rag over the intake....don't use your hand, it may pinch badly...

but do get it checked out..

SamLust · May 24, 2010

Diesel engines have no throttle. Speed/power is controlled by injection of fuel. Fuel injected into the combustion chamber ignites in the heated atmosphere created by compression. Any fuel introduced will burn. In this case, it may have been that your rings, valve guides or some other factor were worn enough to allow lubricating oil to enter the combustion chamber, thus providing fuel and no way to control it. Hence "runaway diesel engine". It is known to happen. The only way to stop it is to somehow choke off the supply of air. Even at that it is usualy near impossible to shut down. The engine keeps going untill something causes it to stop. Like a broken piece. Such as crank, rod, piston etc.

Back in the old days big diesels han "emergency stops" which dropped a throttling plate over the air intake and starved a runaway engine. I haven't seen one of those in years.

First thing I think you might try is turning the engine over by hand. Flip the compression release levers and use the hand crank to turn it oner. It could be enlightening.

Good luck with this one.

Bill1565 · May 24, 2010

a board, even a cutting board laid flat over the intake wil cut off the air. I would not used a rag, would be concerned about getting it back out.

Newbie · May 24, 2010

The first thing to do is find out what exactly it is burning. Fire it up with two people. one out on deck the other (you) down below and see what color the exhaust smoke is if you can. Oil will be grayish blue, diesel is black. Then it's a matter of finding what is happening.

kenn · May 24, 2010

A runaway diesel that wasn't stopped quickly isn't usually good news

As already suggested, I'd try rotating the engine by hand, feeling for compression, then spin it with the starter (compression released and kill lever pulled out) to see if it seems intact. If the engine seems normal at that point, it might be worth trying to start it, no more than 1/3 throttle, with the air filter off and a board or plug ready to block the intake if it runs away again.

... good luck!

woodster · May 24, 2010

you may want to have a good mechanic on hand if you try to restart that engine....if you have never seen one blow from running away with its self its not good and it may sling shrapnal in to some one on explosion and heven forbid killing some one as well ......its nice to be able to work on theses things for ones self ...but when this type of thing is happinging it best to leave it to the pros......better safe than sorry.....this may sound a little harsh but i would rather see you mad at me for scholding on the side of caution as opposed to me having to post condolances on this forum....

regards

woody

druid · May 24, 2010

On an engine with compression release, it's easier to to stop it with CR than trying to choke off the air.

It does sound like runaway - running on crankcase oil instead of diesel (assuming your fuel shutoff actually works). One disadvantage of the mechanical lift pumps in Yanmars is that unlike electric ones, they keep working as long as the engine is turning over.

You could probably safely restart it (although it sounds like Something Bad caused it to stop...) because runaway pretty much needs a hot engine. For sure have a hand on the decompression levers in case it does go off...

druid

Steve Dion · May 24, 2010

If the fuel shut off works, that would be a good place to start. If that does not work, then a towel over the air filter intake should do the job.

The decompression levers are also an option.

Dan Hill · May 25, 2010

Runaway diesels tend to self destruct, throwing pieces of themselves in all directions at high velocities. I would not try to restart this engine again until the cause is found for fear of a pierced hull or body part. If it does run away again the ONLY way to stop it before it dynamites is to stop the air flow into the intake, and that takes you close to the action. A cold diesel can run away also btw. Get a mechanic there! Good Luck!

mcaswell · May 25, 2010

Well damn, I'm scared now. How often does this happen? If my diesel started to run away, it would probably be at least 30 - 60 seconds before I could get down there, get the kids moved to the bow, remove the stairs, open the engine cover, and plug the intake.

--Michael

kloudie1 · May 25, 2010

Fortunately, not often.. and never on a well maintained engine unless something strange happens.. We had a diesel pickup truck drive into a cloud of propane/butane some years back.. The driver got out of and ran out of the cloud before it ignited from scattering engine parts.. That is the only one I personally worked with in 40 years of messing with engines. If you are concerned, you can rig an emergency remote cable stop on the decompression levers.. (should never be used to stop an engine normally) ..

Chuckbear · May 25, 2010

mcaswell said:
Well damn, I'm scared now. How often does this happen? If my diesel started to run away, it would probably be at least 30 - 60 seconds before I could get down there, get the kids moved to the bow, remove the stairs, open the engine cover, and plug the intake.

--Michael

Michael, to ease your fears, in over 35 years of servicing boats of every make and size, both sail and power, and cruising in our own boats for tens of thousands of miles, we have never encountered a run-away engine, nor do we know anyone else that has. So it is indeed a rare occurrence and usually a symptom of neglect. Chuck

Steve Dion · May 25, 2010

Chuck:

Had a friend with one of the one cylinder Yanmars and it has done it more than once.

Diesels will burn anything, so crankcase oil or diesel fuel work just as well.

Texas Lake Sailor · May 25, 2010

In 24 years of working on diesels in the Navy, I only saw one and it as stated was due to poor maintenance & an equipment failure. I running diesel will continue to run on just about anything, oil, fuel or whatever. The best prevention is a well maintained engine. The danger from a diesel is much less than the risks of a gas engine. So do your PM's and you should be ok.

Chuckbear · May 25, 2010

Steve Dion said:
Chuck:

Had a friend with one of the one cylinder Yanmars and it has done it more than once.

Diesels will burn anything, so crankcase oil or diesel fuel work just as well.

I did not say it does not happen, I simply said I have never encountered it. Perhaps your friend needs to have some serious work done on that engine. Chuck

Rick D · May 25, 2010

Just a thought. One way this can occur is to overfill the crankcase with oil. You didn't by chance just change the oil or add to it?

kloudie1 · May 25, 2010

check the lift pump too.. following on Rick and Druid's posts.. if a leaking diaphragm leaked a lot of diesel into the crankcase, it may have led to a runaway.. the engine may have stopped when it burned all the excess fuel.. If it didn't scatter itself, and it can be turned over by hand, ya probably have a chance of it starting again and running normally IF the problem is corrected.. Luck to ya!