SailNet Community banner
  • SailNet is a forum community dedicated to Sailing enthusiasts. Come join the discussion about sailing, modifications, classifieds, troubleshooting, repairs, reviews, maintenance, and more!

Runaway diesel

8K views 49 replies 29 participants last post by  Cap-Couillon 
#1 ·
Harborless's problems with a "runaway diesel" is so odd that I really want to know more. How can this happen when the Governor sets the max amount of fuel unless the governor isnt working? Bristol suggested that overfilled oil was allowing oil to be burned instead leading to runaway. Yes, I can imagine an engine continuuing to run on oil but to run away? I woulda thought that in order to run fast that good properties would be necessary and with just the oil, it isnt being injected right.
I've always found that REALLY understanding symptoms solves 90% of problems so we have to get a solid handle on them.
 
#2 ·
Run away on oil has happened to me once.
I put too much oil in while changing it (boat wasn't level while on the hard), then on my first time out decided to test throttle to max RPM. Frothed it right up. Huge clouds of blue smoke and no throttle control all of a sudden.

The governor doesn't do a thing, it only shuts off/restricts the diesel fuel - so the engine continues to get a full load of 'fuel' from the oil froth.
The fuel shutoff (mechanical and electrical both) does exactly as much good as the governor, none.

Since it's got PLENTY of fuel there and air coming in the engine just does what it is designed to do and runs at full out to use all the fuel coming in, and of course more fuel means higher rpm.

The only way to stop it is to choke air (a rag in the intake) or decompress the engine by tripping the lever on the engine.
You'll need to recognize the condition of run away quick - spinning parts at 4000+ RPM can quickly destroy an engine.

Having had it happen to me just once was enough. I keep a rag zip tied in the the air intake area as well as a zip tie (red) on the decompression lever. It's hard enough to stick your face and hand into a engine compartment with an engine that might be exploding in seconds - doing that and then having to look around for a rag/lever doubly sucks.
 
#45 · (Edited)
Run away on oil has happened to me once.
I put too much oil in while changing it (boat wasn't level while on the hard), then on my first time out decided to test throttle to max RPM. Frothed it right up. Huge clouds of blue smoke and no throttle control all of a sudden.

The governor doesn't do a thing, it only shuts off/restricts the diesel fuel - so the engine continues to get a full load of 'fuel' from the oil froth.
The fuel shutoff (mechanical and electrical both) does exactly as much good as the governor, none.

Since it's got PLENTY of fuel there and air coming in the engine just does what it is designed to do and runs at full out to use all the fuel coming in, and of course more fuel means higher rpm.

The only way to stop it is to choke air (a rag in the intake) or decompress the engine by tripping the lever on the engine.
You'll need to recognize the condition of run away quick - spinning parts at 4000+ RPM can quickly destroy an engine.

Having had it happen to me just once was enough. I keep a rag zip tied in the the air intake area as well as a zip tie (red) on the decompression lever. It's hard enough to stick your face and hand into a engine compartment with an engine that might be exploding in seconds - doing that and then having to look around for a rag/lever doubly sucks.
if the problem is with the fuel delivery system, as mine seems to have been,maybe, the engine will stop running when all injectors are cracked. my engine is perkins .. they are difficult to cut air.

runaway diesel is also caused by engine using its own lube oil to run and continues to increase rpms until overheat and detonation. this one must cut off air flow or ditch compression so it stops or it will detonate and you can lose boat. this cause is not fixed by cracking injectors, i have been advised.

this is mainly caused by excessive blowby, excessive cylinder wear, ring failure...worn, broken, cracked....
mine so far seems to have been fuel delivery initiated.
 
#9 ·
I get ya Ryhs, and my number 1 is the air intake too.
Some diesels don't have the air intake where you can get to it with a rag, but the lever is right there on top.
I'm not a mechanic and don't have enough knowledge about different types of decompression methods, I just know it WILL shut the engine off as opposed to spraying parts of it and the transmission all over the boat.
 
#11 ·
Yes, my manual said the same thing. So the only option is to cut off the air-intake (mine's on the front and easy to get at). Use a rag or a board. Never use your hand.

Not that I have any actual experience with a run-away diesel. I think I'd be too frightened to get anywhere near it.
 
#12 ·
Yes, my manual said the same thing. So the only option is to cut off the air-intake (mine's on the front and easy to get at). Use a rag or a board. Never use your hand.

Not that I have any actual experience with a run-away diesel. I think I'd be too frightened to get anywhere near it.
I'm hoping that I never have to deal with it, but its good to have contingency plans!
 
#15 ·
It needs to be said that if your rag (or parts of it) get sucked into the air intake, it could be a PITA to fix, depending on your air intake configuration (silencer, filter, possibly turbo pump). Sometimes using leather gloves or your hat is a better way to choke off air supply.
 
#16 ·
Badly worn valve guides coupled with very hot engine oil that has been diluted with fuel (sticking injectors) (and as a result the oil level is very high and beginning to froth) is a recipe for runaway. The oil will continue to lubricate...after all diesel is "fuel oil" and a good lubricant...but when the level gets high the crank will begin to act like a food mixer and whip the oil/fuel mixture into a froth. If the crankcase can't ventilate properly pressure can build up in the crankcase and accelerate oil accessing the cylinders through worn internal passages.

Check your oil level regularly. Smell the dipstick to see if you can smell diesel fuel in the oil. Rub the oil on the stick between your fingers when you check it (both cold and hot) so you get familiar with the viscosity of good oil and will recognize if it has been diluted.

Check your exhaust for BLUE smoke. From the interwebz (Neptune Products - no affiliation):

"Blue smoke is caused by engine lubricating oil burning. The oil can enter the combustion chamber from several sources including ..

Worn valve guides, or seals
Cylinder &/or piston ring wear
Cylinder glaze
Piston ring sticking
Incorrect grade of oil .. too thin and getting past rings, or valves guides
Fuel dilution of the oil, making it too thin.
Blue smoke is often evident at cold start, which can reflect reduced oil control due to carbon fouling deposits around the piston rings and/or cylinder glaze (which is actually carbon deposited in the machined cylinder crosshatching. These tiny grooves actually hold a film of oil, which in turn completes the seal between the combustion chamber and the oil wetted crankcase).

Blue smoke should not be evident at any stage.

An engine may actually burn oil without the evidence of blue smoke, because good compression burns oil quite cleanly, however, it is not acceptable for any new engine, or engine in good internal condition to burn large amounts of lubricating oil .. with or without blue smoke."

It is a MUCH better idea to block the air intake of an engine to stop runaway than to use decompression levers. Many of us have no remoter operator on the levers and would have to reach over and "hug" that running-away engine to operate them. Perhaps I should install a cable on my decompression levers? H-m-m-m-m...
 
#17 ·
In our commercial salmon troller, virtually identical to the picture, we had a 3-71 series Detroit (screaming Jimmy) 2 stroke diesel. IIRC it had a "flapper plate", operated by a cable that closed off the intake tract to stop the engine. I don't remember any fuel shut off valve? If I had another diesel I would try to fabricate something similar to be able to stop the engine without being "up close and personal" with it.



Paul T
 

Attachments

#18 ·
In our commercial salmon troller, virtually identical to the picture, we had a 3-71 series Detroit (screaming Jimmy) 2 stroke diesel. IIRC it had a "flapper plate", operated by a cable that closed off the intake tract to stop the engine. I don't remember any fuel shut off valve? If I had another diesel I would try to fabricate something similar to be able to stop the engine without being "up close and personal" with it.

Detroit Diesel Series 71 - Wikipedia, the free encyclopedia

Paul T
This reminded me of an incident my Dad and watched many years ago. We kept our boat at the San Francisco Fisherman's Wharf which was mainly other commercial boats and some charter fishing boats, aka "party boats" or the "puker" fleet". There were no floats, just a series of pilings to tie up to.

One of the party boat skippers was a real cowboy, always coming in way too fast and at the last second dump it into reverse and give it full throttle. Very impressive, good show, old boy. One day he couldn't get it into reverse, slammed the bulkhead and then proceeded to ricochet the boat all over the basin then hitting a boat two spots from us with an awful crunching noise, very bad.

Apparently he had no way to shut down the engine from the helm and his throttle and shift cables didn't work.

Paul T
 
#19 ·
I have written this up before.. but it bears retelling. When I was a tot, my father was chief engineer aboard the USS Holland, a Navy Sub Tender stationed in Rota Spain.

A new guy on the crew was assigned to start up a generator, a "rock crusher". This type of diesel engine has two cranks and crankcases, one up and one down with the pistons coming together in the centre to produce compression and combustion (hence, 'rock crusher"

The new guy was busy talking to one of his new crewmates while filling the upper crankcase with oil and overfilled it. Upon starting, the engine immediatly ran away. After cutting fuel (which did nothing, obviously) they tried to cut air. In an engine that big, you cannot use a rag, it has a flap built into the intake. When they went to use it, they discovered that the flap was missing.

All they could do was evacuate the engine room, alert the bridge and damage control, and wait for it to blow.

Moral of the story, make sure all your safety gear is present and works -before- you have a problem.
 
#20 ·
Likely candidates for runaway are the Pathfinders (V Dub Rabbit) Detroit Jimmies and some English Fords. Dilution of lube with fuel oil from injectors or the return lines into sump can be the the culprit. Dumping the PCV line into the air cleaner can have surprising effect when stuff goes bad too. Pulling the air shut down on a Jimmy will probably suck the gaskets out of the compressor but better than a drive plate through the hull . Fairbanks Morse made the 'rock crusher'
 
#23 ·
Our Jimmy was many years ago and I may be a bit foggy as to how the kill mechanism actually worked. I don't remember a fuel shut off valve, all I know was that it worked, from the wheel. As neutral was extremely hard to find on the Twin Disc clutch it was just easier to kill it once I was in.

Paul T
 
#21 ·
I have not the specialized tools (torque wrenches and such) to get inside the main engine chamber. A specialized Yanmar mechanic is coming down this week. I will be on the boat during the work.
The engine will be fixed, or replaced. The problem WILL be fixed ONCE AND FOR ALL.
I will post a full diagnostic once obtained. Thank you for your interest.
 
#22 ·
frogwatch, your point that in order for an engine to run fast you must properly meter in the fuel and air, and plenty of it makes perfect sense.

But in this case there is an abundance of fuel, so much so that excess "fuel" is exhausted partially and fully unburnt (absolutely tons of smoke is emitted, and raw "fuel" pours out). In the case of a runaway there is plenty of fuel and air is the limiting factor. It just happens that there is enough air to take the engine to an unsafe RPM, and discard the extra fuel.

It is truly terrifying. I keep a piece of plywood near the air cleaner now so that I can use it in the event of a runaway. But I shudder at the thought of having to use it.

It happened to me on a previous boat, a Yanmar YSM15, I overfilled the after an oil change. tarted her up, revved a bit and it ran away. I had nothing handy to stuff in the air intake. I was lucky in that case, It stopped on its own after about 30 secs with no damage. I can tell you that those 30 secs felt like about an hour!
 
#27 ·
Some years ago I had a boat with a Yanmar 3GM30 and I had a small container in the lazerette filled with gasoline for the outboard. The gasoline leaked and found its way into the engine enclosure and just the petrol vapor was enough cause the engine to briefly run away.

It came under control before any damage was done and I learned a valuable lesson about gasoline storage.
 
  • Like
Reactions: davidpm
#28 ·
the 2 cycle gm diesels had a flapper in the intake to shut off the air in case of a runaway. if the air box drains were plugged , oil would build up till the air would blow the oil into the cylinder through the air inlet ports in the cylinder liner. then the screaming jimmy would really scream.
 
#31 ·
only if you managed to get something sucked into the engine.

Generally only 4 things harm engines.

Low/no oil
Overheating
foreign objects ingested
overrunning.

The rest is just wear and tear
 
#30 ·
I took my sewing awl, some #150 thread, a button, a old teak cup holder and a old rubber ball ( old doggie toy ), I ran the string threw the ball ( button keeps string from pulling threw ) screwed the cup holder in the engine compartment close to air intake, ball sit in cup hold so it doesn't get lost and has enough line to reach intake.

May sound a little goofy but, it's there when/if needed.
 
#32 ·
I got to wondering about the decompression lever....

From Yanmar:
Important
Do not stop the engine with the decompression lever. If the decompression
lever used to stop the engine, fuel will spray out and accumulate on top of
the pistons. This will create the danger of an explosion the next time the
engine is started.

From Universal:
DO NOT USE THE DECOMPRESSION LEVER TO STOP THE ENGINE, THIS WILL CAUSE SERIOUS DAMAGE TO THE EXHAUST VALVES.
 
#34 ·
I can see the decompression lever causing fuel issues. All that nasty (and diesel is a nasty fuel) has to go somewhere when you hit that level... and it's under a lot of pressure too, so it is going to go -everywhere-

But I cannot see how it can hurt the exhaust valves. You spin the engine over with the lever open to start, why would it hurt the valves to open it when running?
 
#36 ·
Well, I'm just guessing here, and I'm sure that it depends on the particular engine, but the decompression lever probably holds the exhaust valves open (so that the piston doesn't generate any compression when it strokes upwards, pushing the air and fuel mixture out), and so if you actuate it when the engine is running at speed then it could either A) cause the valve to hit the piston or B) strip out whatever gear/sprocket that is used to actuate the valve to decompress. When you are starting the engine (especially by hand) you are only cranking a few RPMs, when it is running (even at idle) you are at least 500 RPMs.
 
#35 ·
a) Sounds like part of the runaway problems being discussed here may be specific to 2-cycle diesels which have ports in the side of the cylinder and therefore a potential path for oil to come up from the crankcase

b) Also sounds like checking compression and making sure the rings are sealing nicely would prevent oil from getting up into the combustion area

But I'm just theorizing, my experience is only with gas engines (excepting my straight-6 ford when I was a teenager - used to diesel for a few seconds when you shut it off warm :) )
 
#37 ·
I'm not seeing the fuel issue with the decompression lever - the deal is it's a run away engine, you've already pulled the fuel shut off and that didn't work.

Ergo, no diesel getting sprayed anywhere unless it has a magic source.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top