Diesel content in oil

[SailingHarmonie]

Originally Posted by Island Time O25

Pardon my naivete but what is the worst case scenario of diesel in the oil? i.e. the engine will die today/tomorrow, in 1 month, in a year or what?

The WORST case is that the fuel fills the crankcase to the point that the mixture of lube oil and fuel gets sucked into the intake manifold somewhere. That results in an uncontrolled runaway of the engine. You can not control the speed, and you can not stop it. The engine will run faster and faster until it self-destructs. It is scary enough in a road vehicle you can run away from. I can't imagine the terror of this happening on a boat at sea.

If you are not familar with this, search youtube for "diesel runaway" and you will understand the issue...

[skipperpete]

Originally Posted by Island Time O25

Pardon my naivete but what is the worst case scenario of diesel in the oil? i.e. the engine will die today/tomorrow, in 1 month, in a year or what?

The worst case scenario is that the dilution causes the oil pressure to drop and lower bearing seizure occurs, often the low oil alarm is the first warning but different engines behave in different ways. I saw a 4JH5 Yanmar that made oil when the return line leaked (under the valve cover) and gave no sign of trouble until it spun a main bearing cap and effectively destroyed a relatively new engine. A Ford Lehman did the same thing but wore out the rocker gear to the point where there were little deposits of shiny metal filings under each arm. A 4 cylinder Lister engine on a bore pump at Hamilton island was running entirely full of diesel due to an enclosed leaking injector….. fixed the leak, changed the oil and she worked perfectly.
Oil dilution is VERY common in diesel engines ( some more than others) and only occasionally a terminal event despite the abundant urban myths. The spectacular Youtube videos are generally depicting turbo shaft failures or Detroit Diesels with stuck injectors.

[NorthCoastJoe]

If you want to know the worst that can happen. Runaway diesel, my Perkins 4108 had that exact problem. Now it's scrap and I have a new Beta 50 engine.


Factor that into the potential costs. Everything needs to be checked to find the source.
Most crazy runaway ever, you can see the engine start to glow red hot.
https://www.facebook.com/turbokingtv...1893169868092/

[replusted]

I get my oil analyzed every year. The average allowable % of diesel fuel in the oil is less than 3% stated by the laboratory. Mine is less than 0.5%. This may vary by engine model. A good lab will have a database of similar engines and hours run. 15% fuel in the oil is really high.

[geoleo]

Originally Posted by bill424

I am trying to buy a boat with a ~2010 Yanmar diesel. The surveyor's report included oil analysis which shows ~15% diesel in it, which seems bad.

The yard has started taking it apart for diagnosis and don't see anything wrong and think that an oil change is all that is required. Given all the awful things that I was considering as possibilities, I'm relieved but apprehensive.

The boat has been on the hard for two years in NY. Is it plausible that diesel in the fuel lines (or tank) made their way into the engine and thence into the oil?

Any other theories?

Thanks

Yes I had this happen to a Yanmar. The valve push rod slipped off the tappet rocker so the valve was not sealing the cylinder head and firing --the fuel was still being squirted into the compression chamber but not being burned - though still running on 3 cylinders thus it ran down the cylinder wall into the crankcase. Remove valve cover to see if everything is still in place.

[skipperpete]

Originally Posted by geoleo

Yes I had this happen to a Yanmar. The valve push rod slipped off the tappet rocker so the valve was not sealing the cylinder head and firing --the fuel was still being squirted into the compression chamber but not being burned - though still running on 3 cylinders thus it ran down the cylinder wall into the crankcase. Remove valve cover to see if everything is still in place.

You had a valve jammed open(or shut?) and with zero compression and a direct passage to the exhaust or intake manifold and still got fuel into the crankcase?. Did much damage occur to the internals of the engine? How high did the lube oil level get with the un burnt fuel running down the cylinder walls, past the rings and into the sump?

[Fore and Aft]

Bill 424 could the diesel have got in there by accident. I have seen a few really stupid things like that happen. Once we had a tired mechanic accidentally put oil in a radiator that had a remote filler next to the oil filler. Another time I personally stood next to an exhausted mechanic who couldn't get an oil filter undone. After giving up, I politely suggested turning the oil filter the other way and sure enough it came loose. We were all working 90-100 hour weeks so mistakes do happen.
Cheers

[NYSail]

Failed fuel lift pump diaphragm would be the first place I would look. Easy to check for a mechanic….

[Island Time O25]

Originally Posted by SailingHarmonie

The WORST case is that the fuel fills the crankcase to the point that the mixture of lube oil and fuel gets sucked into the intake manifold somewhere. That results in an uncontrolled runaway of the engine. You can not control the speed, and you can not stop it. The engine will run faster and faster until it self-destructs. It is scary enough in a road vehicle you can run away from. I can't imagine the terror of this happening on a boat at sea.

If you are not familar with this, search youtube for "diesel runaway" and you will understand the issue...

Now that you mentioned it.

I had an old MD5A on my first boat, a 1982 27 footer. One of the last ones installed that year. Got the boat in 2006 and the engine looked tired and uncared for. But what did I know? I was a newbie and while handy with tools not really versed in boat maintainence as my, by then, 5-7 seasons of sailing were done on club boats.

After 3-4 seasons of practically maintenance free use (not a good idea) one May, as I was prepping the boat for Spring launch, the diesel did appear to runaway. I was quick thinking enough to shut the valve coming out of the fuel tank. It still huffed and puffed but eventually stopped. I drained the oil. It was grey and sludgy, with consistency of sludge clay. I asked my friend, old time mariner and a diesel mechanic, to help me to diagnose the chances to repair/rebuild this old work horse.

He said that for him the job would be relatively easy, once we took the engine out in few hours but I would have to source the parts he listed. I checked with Volvo and other places and it turned out that the parts would be over $1,500 and not all in stock with 4 to 6 weeks delivery window. Plus his labor. And it still would be a 30 year old engine and underpowered at 7hp. And I would probably lose half of the season to this repair.Did not make any sense. Slapped a bracket on the transom and got a 1990 $200 9.9hp Evinrude and went sailing. Hated that outboard but at least it got me in and out of the crowded mooring field. Sold the boat next season.

[Bellinghamster]

A departure from the OPs question, but since runaway has been mentioned a couple times... the best (and often only) way to shut down a runaway engine is to cut off it's AIR supply. Fuel can come from more than one source: stuck injection pump rack (which shutting off fuel supply line will eventually slow down, but not necessarily before damage occurs), or running on oil/fuel from the crankcase, but the engine only has one source of air and can't run without it. Any engine that sucks intake air through a single hole (older Perkins intake "hoods", Yanmars with a silencer can, etc.) can be easily choked with a block of wood over the hole (I don't recommend using your hand, as tempting as it may seem!). Screened intakes can be slowed down by covering with rags or a towel and shut down with a sturdy plastic bag. Air can still get in through the crankcase breather hose, so that might need to be blocked as well to get the engine to stop completely, but that can be done after the runaway chaos is under control. Good to think through the process and even keep the needed materials nearby, similar to keeping a tapered plug by your seacocks.

[donradcliffe]

Back to the OP, the group has given you the ways that diesel could have gotten into the crankcase. None of them will be solved by an oil change.

[bill424]

It will be interesting to see what the final verdict is from the yard next week. I just wish that there was a way to test for this that doesn't involve sending a sample off for analysis - centrifuge anyone?

[Stewie12]

I have had this problem and it was the seal on the injector pump. The wrong type had been put on.

[Bill_Giles]

It would be worrying if the engine had been run with that amount of dilution. Finding the fault would or could be a lengthy and expensive exercise. My advice is to start looking at other boats.

[sinnerman]

Originally Posted by NYSail

Failed fuel lift pump diaphragm would be the first place I would look. Easy to check for a mechanic….

Ditto.

If it has a mechanical (not electric fuel pump (which I believe most of the older Yanmar's have:

Old boat, rotted diaphragm.
Diesel leakage path is directly to the crankcase.

My two cents

cheers