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Old 01-21-2020, 10:47 AM   #1
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Twin 240 Yanmar Diesels Blow by problem

Hello everyone,

I need some advice, I have a 34 Mainship Pilot, owned her for 5 years. I have put 700 hours on her and she has a total of 1700 hours. I am having a significant drip of oil onto the turbocharger blower from the Crankcase Vent tube. It is leaking into the bilge. I am told that could indicate a need for a rebuild or you can attach a hose to the crankcase tube and route excess to a collection point. I am also told that it seems way too early for the need for a rebuild. I am not burning through a lot of oil,, just enough to be really messy. I check the oil level regularly.

Any advice?

Tish Oleksy
Dolce Vita
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Old 01-21-2020, 11:09 AM   #2
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I'm not familiar with this engine but if it is an open crank case vent design, a collection bottle may solve your issues. Or you could install a closed crank case vent system that routes your blow by to the air intake.

You can check for excessive blow-by by opening the oil filler cap at idle and under load. If there is a lot of oil mist "puffing" you could have a weak cylinder.
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Old 01-21-2020, 11:25 AM   #3
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I would not pipe the oil into the intaKe as it could lead to a runaway if the condition worsens. Many diesels do this but if your engines are suspect, I wouldn’t do it.

Do you ever run these engines or are they lightly loaded? Ever go to WOT?
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Old 01-21-2020, 11:33 AM   #4
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Don't know Yanmars, but a lot of crankcase vents have ways of stripping out the oil while letting the air pass thru. Sometimes with baffles or with some kind of media. Often it looks like steel wool. As time passes, dirt builds on the wool, restricting the opening and causes the air flow to be more forceful. Cleaning or replacing the media sometimes solves the oil dripping problem.
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Old 01-21-2020, 11:51 AM   #5
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We put a Racor CCV system on our Cummins diesel in our motorhome. It filters the oil out before returning the air to the engine. You change out the filter but it is a really long time between changes.
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Old 01-21-2020, 12:05 PM   #6
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Let's first tackle the problem at its source. Often you see a lot of oil in the vent but not exhaust gas blowby as a result of overfilling the crankcase. The crank whips up the excess oil and it goes out the vent. So first do the hand test over the oil filler port and see if you are getting heavy puffs. That is real blowby and strongly suggests worn rings.

If that is the case the engine was run to the pins most of its life which wore out the rings. You can keep running for a while, maybe a long while with an oil separation kit such as Racor, Sbmar and others make.

But if the oil is filled too high, let it drop a quart and see what happens particularly if the hand test above is negative. If the oil diminishes then keep the oil full to that point.

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Old 01-21-2020, 12:18 PM   #7
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Let's first tackle the problem at its source. Often you see a lot of oil in the vent but not exhaust gas blowby as a result of overfilling the crankcase. The crank whips up the excess oil and it goes out the vent. So first do the hand test over the oil filler port and see if you are getting heavy puffs. That is real blowby and strongly suggests worn rings.

If that is the case the engine was run to the pins most of its life which wore out the rings. You can keep running for a while, maybe a long while with an oil separation kit such as Racor, Sbmar and others make.

But if the oil is filled too high, let it drop a quart and see what happens particularly if the hand test above is negative. If the oil diminishes then keep the oil full to that point.

David
Exactly what Dave said
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Old 01-21-2020, 12:27 PM   #8
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I vary the running speeds, but I try every trip to run WOT for an hour or so.
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Old 01-21-2020, 12:29 PM   #9
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I will try that this weekend.
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Old 01-21-2020, 12:39 PM   #10
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How do you check the oil?
My 240 has sealed dip tubes, so I have to pull it out and then check.
If you just pull the stick out it will read low. After the oil relevels you get a more accurate reading.
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Old 01-21-2020, 01:03 PM   #11
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It is not un common for a turbocharger to slobber a little oil out of the intake.
From what you described I would not consider it a problem necessarily.
If nothing apparent comes from the suggestions above, if a strategically placed oil diaper or a piece of one will handle the volume, you might try that first.
A system such as the Racor CCV would certainly take care of any dripping oil.
You can also make your own "catch can". I made one out of a piece of 3 inch PVC pipe, a few fittings and some hose. Oil diaper in the catch device to absorb the oil, and vent the can near an engine room vent.
Hope this helps.
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Old 01-21-2020, 01:42 PM   #12
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I vary the running speeds, but I try every trip to run WOT for an hour or so.
Why do you do that?

I believe that every high output engine has maybe 1,000 hours of usable life at wot. You can use that up by running flat out for 1,000 hours, going slow for 10,000 hours and wot every 20 hours for 10-15 minutes to check that you can reach wot rpms and blow out any carbon, or any combination of the above.

Sounds to me that you may be using it up too fast. How many hours are you running at reduced rpms vs wot rpms. I would consider reduced rpms 2,900 or less. And what is your wot rpm and is it phototach calibrated?

Over propping by even 200 rpm will wear out your engine after 1,700 hours if you are spending a decent fraction at wot.


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Old 01-21-2020, 02:18 PM   #13
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Catch can and keep an eye on it. Oil out the vent isn't necissarily blowby.

Oil with exhaust? sure.
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Old 01-21-2020, 02:31 PM   #14
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1000 hours is about 10 years of the average rec boater’s use. I don’t think his engines will be used up while he still owns his boat so not material. Especially at one hour per trip...? No worries.

Engines are designed to run WOT and it is the best way I have ever heard of to judge the condition of your engines and ancillaries. Many are rated and prohibit more than a certain time at WOT, many are M1 and are “continuous” which means WOT for 24 hours.
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Old 01-21-2020, 03:08 PM   #15
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Because of where I am and what I am doing. If I am cruising I might run at 1800 RPMS for a few hours then make stops along the way. Then I get behind schedule and take off for port or to catch up. Originally I was under the impression, running slow was a good thing, then through forums and the input of other boaters and mechanics found that I should be running WOT more. Trying to balance fuel consumption as well.
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Old 01-21-2020, 03:15 PM   #16
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Engines are designed to run WOT and it is the best way I have ever heard of to judge the condition of your engines and ancillaries. Many are rated and prohibit more than a certain time at WOT, many are M1 and are “continuous” which means WOT for 24 hours.
Here is my point: Say during the life of the boat, he ran for one hour at wot for every 4 hours over a total of 1,700 hours. That is about 425 hours at wot, or almost half way gone. But let's say he is over propped by 200 rpm. That 425 hours easily becomes 1,000 hours equivalent and the engine is now toast.

So yes engines are made to run at WOT but not for long. I recall reading a thread over on boatdiesel about the Navy's 1,000 hour torture test. Much of that 1,000 hours was at wot. The Cummins 6BTA was the only high output recreational type engine that could pass it.

I would expect that any engine that makes 60+ hp per liter would have trouble going 1,000 hours at wot.

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Old 01-21-2020, 03:28 PM   #17
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The operator manual for the 160 Perkins that was oem in my old main ship said WOT for 1 hour then 10 minutes at 200 rpm less then repeat.
The Cummins 6BTA I re powered with said 1 hour out of 8 at WOT.
So 85% of the time at wot for one engine
12.5% at wot for another
What do da book say?
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Old 01-21-2020, 03:39 PM   #18
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I am in the process of installing oil catch cans on my Lehman 135's. There is not a significant amount of oil but enough to make a mess. The vent hoses go from the valve cover to the air filter. I am using a air compressor air filter and currently making a bracket to mount it to the manifold. It has a baffle in it to help separate the oil from the air, a glass bowl, and a drain valve.
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Old 01-22-2020, 07:59 AM   #19
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Thanks everyone!

A quick thank you, I feel like I have learned a lot about this issue. My first time posting a question!
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Old 01-22-2020, 08:24 AM   #20
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A quick thank you, I feel like I have learned a lot about this issue. !
I learned a lot also.

I now know it is either good or bad to run at WOT.

Anything in moderation will be ok.
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