Crankcase Oil Contaminating Yanmar Diesel Fuel

[Compass790]

Thinking more on the problem...lol.
For diagnosis of where the fault lies you could gravity feed both the injection pump & the lift pump with clean fuel from a seperate container & then take off the outlet off the lift pump & the return line from the injection pump & lead into clear bottles & see which one is contaminated with engine oil. All it costs is a bit of hose & banjo bolts & clamps. That would isolate the problem& I know I'm repeating myself partly but it is different as you want seperate supplies & outlets for the 2 pumps

I doubt it's the IP on a 2006 engine but anything is possible.

I'd do this before you remove or install anything but YMMV

[Shaneesprit]

Hmm
Well first if you have gravity, you don’t need a lift pump, I had an electric lift pump, but removed it as my tank is close enough to the engine.
Clean everything, out in the fuel system, don’t leave a drop of contaminated fuel, new filters, and fresh fuel but I think you got this far?
You can reduce crankcase pressure by simply pulling the dipstick slightly out of the tube. Or removing it completely.
Unlikely to be the injection pumps these are normally lubricated with diesel not oil.
Make sure the return lines are clear. Consider new fuel lines.
Then see how it goes, crankcase filters and air filter checked?
Loosening the fill cap or remove the seal again reduce crankcase pressure.
Not sure on your engine but Turbo? Or any kind of regen valve?
But generally fuel systems are completely separate from oil - if the lift pump was engine driven rather than off the fuel pump then I would remove it.
I have removed and blacked off several mechanical pumps on cars in the past, all due to oil leaks into the pump body - buy if you can’t see it then I guess it could in theory get into the fuel, but as you stated it’s gravity - why wouldnt the contents of your diesel tank end up in the sump?

[skipperpete]

I suggest that you don’t pull out the dipstick while the engine is running, the dip tube goes to the bottom of the oilpan and if there is any crankcase pressure, a lot of oil will come out of that tube.

[Sohum]

Originally Posted by skipperpete

I suggest that you don’t pull out the dipstick while the engine is running, the dip tube goes to the bottom of the oilpan and if there is any crankcase pressure, a lot of oil will come out of that tube.

+1. Have u replace the lift pump?

[swordds]

Diesel* Fuel Contaminated With Crankcase Oil: Summary of Troubleshooting and Repair:

First of all let me say the problem is FIXED!!* And since I had spent some effort online searching without success for a similar diesel engine fuel contamination problem I will provide a narrative of the problem and resolution, in the chance that someone else stumbles into a similar problem in the future.

While performing routine maintenance service on my 2006 Yanmar 3YM20 we discovered that the primary Racor 30 micron filter, the secondary Yanmar 10 micron filter and the fuel in the filter bowls were all very black. The secondary filter element had even been “sucked-in” and collapsed on itself (photo attached).

We removed 5 of the approximately 8 gals of contaminated fuel from the tank and attempted to polish the remaining fuel with a portable diesel pump and filter system, but without any visible change to the opaque black fuel color. The other maintenance items were completed including changing the crankcase oil and filling the oil to the high level mark on the dipstick and the boat was taken out for a test run.

After approximately one hour of run time the engine began to loose power and would not accelerate or continuously run above 1,200 RPM (classic fuel starvation symptoms).* Upon inspection, once again the primary* Racor 30 micron fuel filter was black and the secondary Yanmar 10 micron filter was even blacker and the secondary filter bowel was filled with a thick black substance that resembled (color, smell, viscosity,* feel) like crankcase oil.* The dipstick oil level had also dropped from the high mark to half way between the high and low marks. This led to our assessment that crankcase oil was somehow being sucked or pumped into the diesel fuel system. However, while researching the problem I could not find any online references to a similar problem, only references to intentionally adding crankcase oil to diesel fuel or to diesel fuel diluting the crankcase oil, but none regarding crankcase oil entering the fuel system.

We replaced the dirty 30 micron Racor filter with a 10 micron Racor filter and the secondary Yanmar filter with a new 10 micron filter. The fuel tank was emptied and wiped dry and clean and 5 gals of fresh, clean diesel was added to the tank.**

The person (much smarter than me) doing the troubleshooting determined that a likely site for this cross contamination was the fuel lift pump, and even though we couldn’t find any references for this problem a replacement pump was purchased and installed.* After several more hours of engine run time the filters were rechecked and have remained clean and the crankcase oil level has remained stable.* The original lift pump was disassembled and a tear in the pump diaphragm was discovered (photo attached) which we have concluded was the cause of the fuel contamination problem.

[Shaneesprit]

Originally Posted by skipperpete

I suggest that you don’t pull out the dipstick while the engine is running, the dip tube goes to the bottom of the oilpan and if there is any crankcase pressure, a lot of oil will come out of that tube.

Assume you made this statement without any technical knowledge!

[skipperpete]

Originally Posted by Shaneesprit

Assume you made this statement without any technical knowledge!

[skipperpete]

Even ¼ of 1 psi will get oil to the top of the dip tube and possibly everywhere else. The original proposition was that the pcv valve was stuck and crankcase pressure might have been causing lube oil to cross from the injector pump cam box into the attached lift pump.
Pete.

[Compass790]

Great Swordds that you didn't buy a new injection pump as that would have set you back over a boat buck at a guess.
Surprised the lift pump failed so early but that was the only thing I could think of that would account for oil in the fuel. Thought it must be oil & not sludge when you said oil in engine filter was much more concentrated. AFAIK our 1980 Yanmar has the original lift pump & diaphragm so interested the 2006 engine had a diaphragm failure

Glad you posted the result but I have one more question, have you got any blowby? i.e raised crankcase pressure. Just want to know out of interest if that may have been a factor.
Happy sailing ( & motoring!)

[skipperpete]

Well done Compass790, you nailed it in post 5.

[skipperpete]

And Swordds..... thanks for the interesting thread and final solution. Good work.
Pete.

[swordds]

Thanks again for all of the interest and every suggestion. I myself thought the lift pump was a long shot but fortunately I had help from a much more capable person. Three minor additions: 1) Surprisingly to me there’s was no detectable crankcase pressure, I removed the oil filler cap and even a very fine tissue paper did not indicate any pressure. 2) The lift pump was easy to remove and replace, a socket wrench would not work but an open-end 10mm wrench held at an angle was all that was needed and nothing else on the engine had to be removed for access. 3) The online service manual was useful (though this specific problem was not covered) and is also enjoyable to read and the drawings in the online parts manual are works of draftsmanship art.

[Wotname]

Originally Posted by swordds

Thanks again for all of the interest and every suggestion. I myself thought the lift pump was a long shot but fortunately I had help from a much more capable person. Three minor additions: 1) Surprisingly to me there’s was no detectable crankcase pressure, I removed the oil filler cap and even a very fine tissue paper did not indicate any pressure. ........

I think you would need to close off the crankcase breather before you detect any possible crankcase pressure at the oil filler cap.

The attached is from the 3YM manual.

[Compass790]

Originally Posted by skipperpete

Well done Compass790, you nailed it in post 5.

Thanks for the kudos skipperpete, means a fair bit coming from you.
Think I only got it scenario 1/2 right as it appears the excess crankcase pressure is not needed to get the issue. Still it was close.

It was post #6 my slightly educated guess. Still scratching my head how it's not the usual diesel in the sump diaphragm failure telltale.


Enjoyed the thread made better by swordds descriptive feedback.

[Wotname]

I dunno why but I wonder if the fact the lift pump is driven by a cam in the injection pump rather than the more conventional cam on the camshaft makes any difference.

?????