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Old 01-10-2014, 11:25   #1
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Advice on Yanmar 3gm30 Oil Leak?

I've removed the crankcase breather vent and the tube, and neither was clogged. I ran a lighted mirror and my fingers along the line running from behind the starter to the main bearings, and it is not leaking oil. I found a slight leak from the stern-most, port-side corner of the oil pan and tightened the bolts about 1/8th, and that leak seems to have stopped.

But unfortunately, I still have an oil leak. It runs down the back of the engine block and seems to be coming from somewhere up inside where the block attaches to the flywheel housing.

So, my question is: Should I do a compression test to indicate whether the rings are shot and then, if they are, should I assume that all seals and gaskets are fine and that the air being pumped into the lubrication system is forcing oil out through perfectly good seals, or should I go straight to replacing the seals (which is gonna get ugly)?
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Old 01-10-2014, 11:34   #2
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Re: Advice on Yanmar 3gm30 Oil Leak?

Run the engine... how much blow by are you getting out of the oil filler or CC Vent? There shouldn't be much.
Is it possible the oil leak is where the head joins the block in the back? You may only need a head gasket if there is not a lot of blow by.
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Old 01-10-2014, 11:37   #3
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Re: Advice on Yanmar 3gm30 Oil Leak?

Thanks, Cheechako. Would I be able to see the rearmost portion of the head gasket with a lighted mirror? If so, I'll look. On your advice, I'll also check for blow-by at the filler, the dipstick and the vent tube.
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Old 01-10-2014, 11:44   #4
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Re: Advice on Yanmar 3gm30 Oil Leak?

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Originally Posted by DennisM View Post
Thanks, Cheechako. Would I be able to see the rearmost portion of the head gasket with a lighted mirror? If so, I'll look. On your advice, I'll also check for blow-by at the filler, the dipstick and the vent tube.
I cant remember, no longer have a 3GM30, but I suspect you should be able to see the line where the head and block meet back there.
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Old 01-10-2014, 11:45   #5
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Re: Advice on Yanmar 3gm30 Oil Leak?

Thanks again! I'll look.
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Old 01-10-2014, 11:51   #6
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Re: Advice on Yanmar 3gm30 Oil Leak?

Our Yanmar3GM30f had an oil leak due to a leaking gasket hidden by the cover for the manual starter. I unscrewed the cover and replaced the gasket. This stopped the Oil leak Click image for larger version

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Old 01-10-2014, 11:55   #7
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Re: Advice on Yanmar 3gm30 Oil Leak?

Thanks, Carlager. My leak is definitely coming from the top half of the rear of the engine, however.
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Old 03-10-2014, 01:31   #8
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Re: Advice on Yanmar 3gm30 Oil Leak?

Have you checked the area where the rocker/bonnet/valve cover sits on top of the head? I had a leak issue with that recently.
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Old 04-10-2014, 06:07   #9
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Re: Advice on Yanmar 3gm30 Oil Leak?

I haven't, Mtarcher. Thanks for the tip. I'll check that today, along with the other great suggestions I've gotten. Thank you, everyone!
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