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Old 14-06-2024, 06:11   #1
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Yanmar ysb8 blows oil out breather tube

Ysb8 blew oil out the drain pipe, put a good plug on that and leaned out the breather assembly since I couldnt even feel air coming out of it, not surprisingly oil now blows out the breather pipe, about a pint in 10 minutes at idle ( boat is on the hard)
Didn't have any signs of oil last season. Engine starts right up, sounds good, no smoke whatsoever. Next step? Pull out piston and inspect the rings?
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Old 14-06-2024, 06:35   #2
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Re: Yanmar ysb8 blows oil out breather tube

Have you checked the oil level? Is it overfilled?

It is possible that you're getting water, causing the oil to rise to the top and, when overfilled, starts coming out the breather?
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Old 14-06-2024, 07:10   #3
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Re: Yanmar ysb8 blows oil out breather tube

Oil level is good and as I've run the engine the level only goes down. The oil is a gray color right now.I don't know if that's the normal progression to black for fresh oil
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Old 14-06-2024, 08:02   #4
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Re: Yanmar ysb8 blows oil out breather tube

Brown oil almost always means water is mixed in it
A blown head gasket could result in both oil in water and combustion gas getting into crankcase. I'd pull the head off and have a good look at the gasket for any breaches. If you find evidence, I'd recommend leaving rings alone unless the cylinder walls are rusty/pitted. Water in the cylinder causing a minor hydrolock could be the cause of the blown head gasket), or could be the path of water into the oil - check cooling exhaust systems carefully!
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Old 14-06-2024, 19:50   #5
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Re: Yanmar ysb8 blows oil out breather tube

I would say you have a blown head gasket. Not at all uncommon on these engines, gray oil means it has water in it. They have 23:1 compression & vibrate a lot so hard on head gaskets. Can still start easy with a leaking head gasket. Used to sell parts for them so have knowledge of the engine. My advice when fitting new head gasket is to uses Loctitie 518 or permatex equivalent on mating surfaces & you will have less trouble. Also retorque head after 10 hrs running.
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Old 16-06-2024, 04:53   #6
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Re: Yanmar ysb8 blows oil out breather tube

I forgot I had water in the oil from from running the engine off a bucket in the cockpit above the engine and then left it sit up there for a while. Ive since run the engine and changed the oil a few times. No more signs of water in the oil.
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Old 16-06-2024, 04:54   #7
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Re: Yanmar ysb8 blows oil out breather tube

I forgot I had water in the oil from from running the engine off a bucket in the cockpit above the engine and then left it sit up there for a while. Ive since run the engine and changed the oil a few times. No more signs of water in the oil. Could stuck rings be the culprit?
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Old 18-06-2024, 19:21   #8
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Re: Yanmar ysb8 blows oil out breather tube

You havent had the access plate to the conrod off by any chance have you?
If you put that back on upside down you will blow oil & it can lead to engine runaway. This has happened a few times to customers.
Have you checked exhaust mixing elbow for leaks? If oil staying black should be ok but needs to be checked occaisionally anyway. Do you have service manual?
Still think head gasket most likely cause if conrod access plate not upside down.
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