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Old 07-16-2019, 04:24 PM   #1
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Yanmar breather tube puke slight oil ...

My 4Jh2 series engine when run long, will have a bit of oil coming out of the breather tube that comes from crankcase and runs to intake turbo. Also, the screen for air intake will have a thin film of oil over it ... should I be concerned or is this not such a big deal?

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Old 07-16-2019, 05:10 PM   #2
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Not that big a deal. Maybe you are getting some piston ring blowby into the crankcase that is causing it to carry oil over. Do this:

Take the oil filler cap off and under a bit of load either at the slip tied off well in gear or underway at 1,200 rpm, put your hand over the filler hole. You should feel at best slight exhaust pulses. Any significant pulses means your rings are beginning to go.


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Old 07-16-2019, 05:50 PM   #3
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A four cylinder will throw out oil from the fill cap even if everything is right, so not a real valid test. That test is valid for a 3, 6 or 8 cyl.

A little oil spittle out the blowby tube is normal.
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Old 07-16-2019, 07:00 PM   #4
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Any crankcase blow-by is a cause for concern. Blow-by is from piston rings leaking or other excessive pressures in the crank case.

If piston rings are leaking it is s sign that the rings are stuck or worn, and further maintenance may be needed. The further part may be an engine rebuild for $$$$$$$$$$. The wise thing to do is have a certified technician from your engine manufacture to diagnose the blow-by and correct the problem before it get worse.
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Old 07-17-2019, 10:22 AM   #5
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If you take the average truck engine and drop it in a boat, it is usually tilted to align the shaft. This means the oil is now deeper at the back of the sump and now the crankshaft is immersed in oil. This leads to significant aeration of the oil and blow-by. Get one of the various recovery systems and filter the oil out of the discharge and return it to the sump.

Summit Racing is a good online source.

A common problem with Lehman engines is the marinizer forgot to re-mark the dipstick, resulting in too much oil being put in the pan with the incorrect markings; weeping seals and high oil consumption is a result. Many owners know their Lehmans will seek their own oil level and stay at that level until the next oil change.

At least once in your maintenance cycle, add the correct amount of oil as per the manufacturer, wait a half an hour and then look at the dipstick - is yours correct? You might need to remark yours.
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Old 07-18-2019, 02:25 AM   #6
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X 2 what Xsbank said.
run it, letting the oil level go down, and you’ll likely find a spot where it stops receding.
This is where your dipstick should be marked.

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