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Old 07-12-2015, 05:39   #1
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3GM30F oil in exhaust

My 3GM Was removed for paint job, it ends replacing all hoses and seals, even head gasket, cylinder removed por inspection injector tips replaced,. when the engine starts after 10 to 15 minutos dark oil starts to come out of the No 1 Cylinder, and at the same time the oil press drop a bit (5 or 6 Psi), engine is out of the boat in a test bench, removed the head and the top of the No 1 Cylinder was dry only light blak dry smoke on top of it.
does anybody have any clue on this?

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S/v AVAROA
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Old 07-12-2015, 06:12   #2
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Re: 3GM30F oil in exhaust

Where exactly does the oil come out?

Is it from a passageway on the head? From the head gasket?

Is it actually lubricating oil or something that when it's hot flows.....if this, the associated drop in oil pressure is normal as the.? As the oil warms it thins and will take less pressure to circulate.


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Old 07-12-2015, 07:21   #3
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Re: 3GM30F oil in exhaust

The oil comes out of the exhaust hole on cylinder number 3, after removing the head de piston top is dry as well as the exhaust valve. make me thinkof a cracked head, i replace the head for a overhauled one , i get from e bay and the problem persist.
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Old 07-12-2015, 07:39   #4
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Re: 3GM30F oil in exhaust

So it's either cylinder one or three?

Have you shuffled injectors to see if one is injecting too much fuel? Or not atomizing fuel?

Otherwise it could be a valve stem seal or or rings.


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Old 07-12-2015, 07:55   #5
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Re: 3GM30F oil in exhaust

injectosr were just serviced, they replace the tips at a certified bosh repair station using yanmar original parts, anyway i removed them and tested again they are in perfect shape. valve steam seals were replaced for new in both heads, and the problem persist

i have put this engine apart a least 3 times in 12 years i owned it,and is the first time i can't find the source of the problem


you mentioned o rings, which ones?
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Old 07-12-2015, 09:27   #6
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Re: 3GM30F oil in exhaust

Are you positive the exhaust valve seals are not leaking at all? That sure sounds like a bad seal if the cylinder is clean.

What are the compression numbers like?

Are you positive the injectors are seated correctly?

When you have taken apart the same motor many times, it is usually the small stupid stuff that gets you.

A bad valve seal may not notice much when running, but after stopping the engine can dump oil that will get pushed out into the manifold on next start when the valve is open after stopping and the oil pressure comes off.
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Old 07-12-2015, 09:43   #7
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Re: 3GM30F oil in exhaust

Oil gets sucked down the valve stem if the O ring or diva cup (different engines) is damaged or improperly installed .Most likely happening here.
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Old 07-12-2015, 10:18   #8
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Re: 3GM30F oil in exhaust

You've checked all the usual suspects and I wouldn't get too concerned about a 5 psi drop in oil pressure, as the oil warms up. (for example, I run the engine for about that amount of time before changing the oil and that makes a huge difference in how much easier it is to pump the old oil out).
As I recall, this is an indirect injection type engine. It looks like you have a case of excessive un-burned fuel, as it only comes from that one cylinder, so I would check the condition of the pre-cup and its' sealing surfaces. It could be that there is not much accumulation of oil, or fuel, because you have only run the engine for such a short time and fuel would tend not to accumulate as much as oil would. You should be able to remove the injector and then extract the pre-combustion chamber.
Let me know what you find.
Hope that helps.
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Old 07-12-2015, 13:08   #9
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Re: 3GM30F oil in exhaust

Thank you all for your posts,
in order to answer your questions i need to wait for the week end, to get where the engine is and perform some test on it, i will do and post the findings,once again,thank you all
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Old 07-12-2015, 15:21   #10
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Re: 3GM30F oil in exhaust

Had a similar problem with my 1 GM. Turned out to be a cracked piston. Not visible unless you squeezed the piston skirts and held it in bright sunlight. The very fine crack went across the piston top. Sump oil appeared inside the actual air intake port! The engine still ran but it was obviously "sick" - blue smoke and oil consumed.
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