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Old 10-06-2021, 19:22   #1
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Crankcase Oil Contaminating Yanmar Diesel Fuel

My 2006 Yanmar 3YM20 diesel fuel has turned black and the secondary fuel filter is filled with what appears (by looks, feel and smell) to be engine crankcase oil. In addition, after two hours of running about 1/2 quart of oil has disappeared from the engine. I have found several discussions of diesel mixing into and contaminating the crankcase oil (in which case the oil level in the crankcase increases) but not vice versa - oil leaking from the crankcase into the fuel tank (in which case the crankcase oil level decreases). My first thought is to replace the fuel lift pump. Any others have experience with a similar problem or other thoughts on cause and correction?
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Old 11-06-2021, 04:43   #2
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

You are looking for a place that the two come together, and where the fuel system can apply a suction to the crankcase oil. The oil seal on the lift pump shaft would indeed be the likely bet. If the shaft is bad, yes, replace the pump, but most likely if this is the source of the problem all you need do is replace the seal. That's cheap, and lets you test the hypothesis.
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Old 11-06-2021, 05:22   #3
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

Hmm... While I understand the logic, I doubt it will be the lift pump and certainly won't be the shaft seal - as it doesn't have one. The lift pump is a conventional diaphragm pump, lever operated and driven by an eccentric cam.

However I'm out of ideas of what would be the cause. Are you sure it is engine oil in the filter and not some type of contaminated diesel (?).

From the 3YM service manual...
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Old 12-06-2021, 06:03   #4
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

Thank you for your replies. I am not sure of anything except that I have a problem and my engine is marginally and unreliably functional. My first solution attempt was to remove most of the contaminated diesel, to replace the severely fouled/blackened fuel filters and to treat the remaining fuel with diesel biocide. That did not solve the problem. Changing the lift pump (an admitted long-shot) and totally draining the contaminated fuel system will be my second attempt (I am currently waiting on the part which will take several days to arrive). If (when?) that doesn’t fix the problem my next step will be to search for a Yanmar mechanic with the experience, tools and skills to dive deeper into the engine. I hope to report the final solution in the relatively near future.
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Old 12-06-2021, 17:11   #5
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

Does the injectors return line go to the secondary fuel filter or back to the tank?
I dont have a 3ym20 workshop manual to try & nut out your problem. It's a tough one for sure, hard to see how engine oil could get in fuel.

Good idea to start with lift pump as thats a lot cheaper, never heard of it sucking in engine oil but cannot say if its impossible.

The injection pumps bottom end is bathed in oil but cant see how it would get into suction side.
Surprised you havent got more responses. Wont be simple for a mechanic to diagnose I suspect but he might take a shotgun approach & replace parts ( likely injection pump& or lift pump) until he hits the right one. Will think on it a bit & get back to you if neuron transmitters fires up.
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Old 12-06-2021, 17:50   #6
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

Have a possible scenario for your problem. I see the lift pump is mounted on the side of the injection pump ( found 3ym manual ) Is the crankcase breather blocked? you could have oil forcing its way through the injector pump drive shaft into the the lift pump when the engine is running if it has high crankcase pressure & a faulty diaphragm. I can send you a copy of the workshop manual for free if you PM me with your email address. It tells you how to check lift pump but if you have bought a new one I guess it doesnt matter.
It probably tells you about crankcase breather though & I think every boat owner who cruises away from help should have a service manual.
Worth a shot checking yr breather anyway.
It looks like your injector return line goes back to lift pump so I dont know how your fuel tank could get contaminated though. Thats the gaping hole in the theory.
Please confirm where return line from injectors goes.
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Old 12-06-2021, 18:03   #7
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

disclaimer first, I am not a mechanic, and never had that engine.

But you can find out a few things first before you spend money.

If the fuel filter is contaminated, with stuff (you said likely engine oil) that stuff must be present in the fuel lines and therefore fuel tank. replace your filter(s). Check your fuel line between filter and tank, make sure that contains clean fuel.
Then check your tank what is in it. If dirty go to next point.

If it is contaminated, then use your other tank (if you have two fuel tanks) or a jerrycan to draw/suck up clean fuel.

Remove the return fuel line and replace with one that that goes in a clean jar/container (ie a litre of two in size). There is no pressure on the return line, and even air leaks in this line does not matter, cheap hose will do.
Run the engine and see what comes out of the return line.

If clean fuel goes in and dirty fuel comes out...... then the dirt/contamination comes in between these two points. Check lines between filter and lift pump, check lines between lift pump and secondary filter, check line between secondary filter and injector pump.
Maybe that is a way of finding where the contamination enters the fuel systems?

Hmmm, dirt in fuel is not good for the injector pump
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Old 12-06-2021, 19:17   #8
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

Thanks Compass790 and HankOnthewater! I will not have the new pump in hand until the middle or end of next week and until the new pump is installed my plan is to leave the entire fuel system (including the tank, fuel lines and filters) drained and empty, but while waiting for the part I will research checking the crankcase pressure concern. And yes, the fuel return line goes to the lift pump and not directly back to the tank.
Another significant concern is that because of the engine installation in my Alberg 30 it will be impractical for me to remove and replace the lift pump (without removing the engine). I can barely even see the pump with a mirror much less access the bolts with a wrench. “Where there is a will”, etc. but I will wait until I have the new pump in hand before attempting to remove the existing pump.
Another thought - Since my fuel tank is located several inches directly above the engine, is a lift pump even necessary or is it possible to just gravity feed the injector pump? And if I were to bypass the lift pump (by either gravity feed or electric fuel pump) can I bypass the mechanical lift pump without removing it?
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Old 12-06-2021, 19:32   #9
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

Quote:
Originally Posted by swordds View Post
Thanks Compass790 and HankOnthewater! I will not have the new pump in hand until the middle or end of next week and until the new pump is installed my plan is to leave the entire fuel system (including the tank, fuel lines and filters) drained and empty, but while waiting for the part I will research checking the crankcase pressure concern. And yes, the fuel return line goes to the lift pump and not directly back to the tank.
Another significant concern is that because of the engine installation in my Alberg 30 it will be impractical for me to remove and replace the lift pump (without removing the engine). I can barely even see the pump with a mirror much less access the bolts with a wrench. “Where there is a will”, etc. but I will wait until I have the new pump in hand before attempting to remove the existing pump.
Another thought - Since my fuel tank is located several inches directly above the engine, is a lift pump even necessary or is it possible to just gravity feed the injector pump? And if I were to bypass the lift pump (by either gravity feed or electric fuel pump) can I bypass the mechanical lift pump without removing it?

Yes it should be possible to do away with lift pump or bypass it if tank is higher than engine. I would certainly try it if engine removal is necessary to get at lift pump. Try hankonthe waters suggestion first ( with filtered fuel ) If gravity feed proves problematic you can get cheap 3-5psi 12v electric pumps which are fine for fuel delivery to injector pumps.
Gravity feed should be fine AFAIK.
You may have to block the inlet & outlet of the lift pump if oil is leaking in to it. I would be tempted to remove lift pump, if you can without engine removal, & just put a cover plate on it.
Sounds like a nightmare engine noroom
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Old 15-06-2021, 05:55   #10
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

Occasional Update: (Because I am always disappointed when trouble-shooting advice is requested but the ultimate solution - assuming there is one - is never presented).
Current Status: The replacement lift pump is on order, cost is approximately $150 (US), “shipping and handling” is not yet fully determined because the delivery is estimated as one and one-half weeks but I have asked for that to be expedited if possible. Both the primary Racor and secondary Yanmar fuel filters have been replaced but the 15 gal fuel tank is empty and open so I can have a final inspection and wipe/dry-out after the new pump is installed.
Future Plan: When (if?) the new pump is installed (see prior concern regarding accessibility) and the engine is running with fresh fuel I will assess the crankcase pressure breather and run the engine to test the “solution” or continue trouble-shooting the problem
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Old 15-06-2021, 06:02   #11
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

in the mean time .. if your fuel is still black .. you need to address that as well. and welcome to the world of working on parts you can only see using a mirror
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Old 15-06-2021, 06:42   #12
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

Thanks, the entire ~ 8 gals (- 30 liters) of contaminated diesel fuel has been transferred to the very helpful local boatyard. They keep a 55 gal waste fuel drum and when the waste fuel drum is full it is probably transferred to a commercial hazardous waste management company.
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Old 15-06-2021, 09:03   #13
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

Sorry, I am confused.

You have 2 fuel tanks and there is contamination in both???

I must have miss read something?
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Old 15-06-2021, 09:10   #14
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

Oh no, just one 15 gal fuel tank, the other fuel container that I confusingly mentioned is a 5 gal fuel (jerry) can.
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Old 15-06-2021, 09:26   #15
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Re: Crankcase Oil Contaminating Yanmar Diesel Fuel

So at this point your fuel is empty? so will be very clean.
I was going to suggest you fill a jar with your tank fuel and leave it overnight to see if the black engine oil separates from the fuel. Then you would know if it was engine oil.

In the meantime, you could bypass the lift pump and put in a $20 NAPA electric pump instead. You can always use that as a priming system for when you change filters anyway.

I have seen old black/brown diesel fuel before and adding a biocide etc may kill the stuff but it wont make it look good/ or remove the junk. It's just dean now. Biocide is best used to keep it from forming in the first place.

I would check out the crankcase breather system. I dont know if you engine has a valve in that breather or not...?
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