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Old 11-15-2013, 02:58 PM   #1
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Oil Analysis show fuel dilution

hi all - new to diesel marine engines so forgive me if I ask a stupid question or two.

Recently purchased a Nordic Tug with a Yanmar diesel in it. It has been repowered prior to purchase with approx. 875hours on it. The first baseline engine oil sample that I had analyzed shows 3.5% engine oil dilution. The maintanence logs show the oil has about 50 hours and 12 months time on it.

Should I be worried about this level of dilution. I know a diesel will tolerate up to 5% dilution but anything over 2% is cause for concern in my book. All the other analysis items look good. No water or glycol in oil, all wear metals within tolerance etc.

I will change the oil since it is due for a chance (12 months old) and then take another sample after running it for a while. I will then know both the load the engine is under (how much idle vs loaded use) and the true state of the oil. Not that I don't trust the written maintenance log but no substitute for a known starting place.

Any thoughts from those much more experienced in these things?
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Old 11-15-2013, 03:26 PM   #2
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Congratulations on your purchase. I'm not sure if it's a cause for concern, but am very familiar with oil sampling. Building a trend is the most useful information you can get, which you will have with future sampling. I pulled engine/ hydraulic samples on a Cat D5C Monday and mailed to the Cat dealers oil lab here in Louisiana- cause they know the parts that make up those compartments. I would think someone versed on your brand of engine would be a better choice to send samples to.
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Old 11-15-2013, 04:19 PM   #3
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Mine came back at 3.5% on a 1983 120 Lehman with 200 hours on the oil. The report says it should be under 2.5%. I'll monitor it and see how the trend goes. The other engine is well within specs.
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Old 11-15-2013, 05:49 PM   #4
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3.5% fuel dilution is way, way too high to just monitor and wait and see. There are two typical sources for fuel dilution: one is bad, but the other, real bad.

The bad one and probably the most likely is a busted diaphragm in your mechanical fuel pump. Easy to fix.

The very bad one is one or more bad injectors that are beginning to "hose" fuel. That is dumping more fuel and in a bad spray pattern than can be completely burned. The unburned fuel leaks by the rings and contaminates the oil.

In severe cases the excess fueling under high power can burn and melt the piston and valves.

So check your fuel pump and hopefully that is the cause. If not, get your injectors tested. One symptom of a failing injector(s) is a diesel sheen on the water behind the exhaust. Another symptom is hard starting.

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Old 11-15-2013, 07:41 PM   #5
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If the injectors were serviced before the last oil change an additional possibile source is the injector leak-off tube, either at the injectors or at the fitting through the head. Bob Smith recommends pressure-testing by disconnecting the leak-off line from the injector pump return line and checking the pressure drop rate, but you would want to call American Diesel for specifics.
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Old 11-15-2013, 08:45 PM   #6
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If the injectors were serviced before the last oil change an additional possibile source is the injector leak-off tube, either at the injectors or at the fitting through the head.
I'm pretty sure that's where mine is comming from (at the injectors).
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Old 11-16-2013, 11:34 AM   #7
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Yeah, 3.5% concerned me. Yanmar recommends oil change and monitor. I may pull the mechanical fuel pump just to either fix it or rule it out as the culprit. If the fuel dilution stays higher than 2.5% AND the engine gets used instead of just idling, the next thing to pull and have serviced are the injectors. Really don't want the fuel dilution continuing given the catastrophic damage it can do to an engine. The one saving grace is that all the wear metals are well within spec so it appears that the lubrication is sufficient. If I had high fuel dilution AND high metal wear in the oil then I would immediately tear things down.

thoughts on this approach?
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Old 11-16-2013, 12:13 PM   #8
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Operating habits can sometimes add to the fuel dilution question. Long runs at normal temperatures should burn off any incidental fuel dilution. Excessive dock idling can add incidental fuel dilution. If you have no obvious injector or lift pump issues monitor your changed oil after a long all day run at cruise RPM. Cat SOS is the monitoring group of choice, who are you using?

There are many Yanmar guys on boatdiesel.com - post the same question there. You've already heard form a solid Yanmar guy, D Marchand.
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Old 11-16-2013, 12:19 PM   #9
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Agreed, plan to change oil and filter, then run the engine thru a normal day and pull another sample as see where I am. Yanmar suggested excessive idling as a potential cause for fuel dilution. Thanks the the advice
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Old 11-16-2013, 01:56 PM   #10
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I saw Eric's (Ski from NC) post on your question over on boatdiesel. Eric is a real pro and I would bow to his advice.

But check the fuel pump diaphragm. Easy to do.

There is also a red neck (as Eric calls it) test for fuel dilution. Take a drop of lube oil and put it on a clean piece of paper towel. If you have significant dilution (and I don't know what significant means), the drop will form a halo which is diesel fuel.

You could monitor the situation using this test to see that happens. Run the engine long and hard and maybe the diesel will go away.

David
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Old 11-16-2013, 04:17 PM   #11
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Originally Posted by djmarchand View Post
I saw Eric's (Ski from NC) post on your question over on boatdiesel. Eric is a real pro and I would bow to his advice.

But check the fuel pump diaphragm. Easy to do.

There is also a red neck (as Eric calls it) test for fuel dilution. Take a drop of lube oil and put it on a clean piece of paper towel. If you have significant dilution (and I don't know what significant means), the drop will form a halo which is diesel fuel.

You could monitor the situation using this test to see that happens. Run the engine long and hard and maybe the diesel will go away.

David
RickB described the "poorman's litmus test" a few months back...some search engine genius may be able to find it quickly....

I would...it's but my first time off this month and headed for the winter season dock get together dinner....
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Old 11-17-2013, 07:02 AM   #12
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Oil is cheap , esp in minor quantities , just change it more often if you cant find the cause without a tear down..
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