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Old 30-07-2020, 10:23   #16
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Re: Yanmar 2GM20F - treatment for blowby

Thanks for the replies so far. More answers:

Air cleaner was good last time I checked but I will double check for any kind of blockage. From what I could see, the breather tube is clear but I didn't check where it enters the intake, just that gas was coming through the tube from the cranks case.

I will double check throttle linkages but I've messed with these before and pretty sure that's not it.
I checked the tappet clearances 2 years ago, expecting to adjust but they were at spec. Stern gland stays very cool.

Again on hours, I think this engine has seen light use over its 34 yrs but no meter/guage. I expect more problems from probable periods of underuse. I doubt it has 2000 hrs on it.
I picked up a laser/tachometer to check that the gauge is giving me accurate RPM's - I'll test that this weekend.

I have not cleaned the injectors - is that something requiring professional servicing or do I just pull them myself and...?

As I have said, the problem isn't "bad" but if I can put off engine disassembly/rebuild, its worth any steps that others have taken. I'll pursue a compression test after some of the steps listed here, and perhaps the injectors?
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Old 30-07-2020, 11:05   #17
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Re: Yanmar 2GM20F - treatment for blowby

All great ideas but I would check the mixing elbow. If you have the U-type elbow, it's only good for 4 to 5 years tops, if could be causing back pressure if it's plugged.
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Old 30-07-2020, 11:49   #18
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Re: Yanmar 2GM20F - treatment for blowby

Quote:
Originally Posted by dennismenace111 View Post
Youre not excessively burning oil...no smoke.. just a few hundred RPM drop at WOT? Have you cleaned the contacts on the tach sensor? My 2GM20F has similar issues but Im also loosing about 1/2 cup of coolant every 4 hours of running. I keep extra oil and a full jug of coolant on the boat.

Ive checked the breather as well to see if its open and functional... I was surprised that it was quite dry inside instead of wet oil. Maybe I should pull the tube off of the outlet and run the engine to see if Im getting airflow out of the breather.
Dennis, if you are loosing coolant I might torque the head down if that don't work check the head gasket.
Good luck!
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Old 30-07-2020, 12:23   #19
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Re: Yanmar 2GM20F - treatment for blowby

Take the tube off and blow through it. Or just replace it since the tube/hose is less than $2.00
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Old 30-07-2020, 16:23   #20
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Re: Yanmar 2GM20F - treatment for blowby

Quote:
Originally Posted by SSAsailor View Post
Thanks for the replies so far. More answers:





Again on hours, I think this engine has seen light use over its 34 yrs but no meter/guage. I expect more problems from probable periods of underuse. I doubt it has 2000 hrs on it.
I picked up a laser/tachometer to check that the gauge is giving me accurate RPM's - I'll test that this weekend.

I have not cleaned the injectors - is that something requiring professional servicing or do I just pull them myself and...?

As I have said, the problem isn't "bad" but if I can put off engine disassembly/rebuild, its worth any steps that others have taken. I'll pursue a compression test after some of the steps listed here, and perhaps the injectors?
Sorry I had a bit of a brain fade, injectors & tappets won't affect blowby, was thinking about power loss but since you've had an increase in blowby maybe Cheechako in post #9 is onto the cause.
However might be just a blown headgasket if its leaking into a pushrod gallery
Will be a bummer if it is but that will have to be checked with a compression test.
Wont hurt to check injectors as a maintenance item, if you don't have a workshop manual I think you can download one from CF library. They are easy to strip & clean, there are youtube vids on doing that.
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Old 30-07-2020, 17:39   #21
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Re: Yanmar 2GM20F - treatment for blowby

I would add some catalyst to the fuel, a couple of tanks full at least, and set off on a long burn with the engine working hard. If that makes no difference, and the blow by is worse, then your engine may have been overheated at some time or other and the rings lost a bit of tension. On the other hand, a Gardner in one of my friends' ex cray vessels was running very poorly, low on power, burning oil, and they expected it needed an overhaul, but catalyst and a Bass Strait Crossing under full load stopped it all and the engine then ran really well.

I would add NOTHING to the engine oil unless the engine manufacturer approves of it, and I would use only the currently recommended oil..
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Old 30-07-2020, 18:46   #22
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Re: Yanmar 2GM20F - treatment for blowby

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Originally Posted by Mike Banks View Post
I would add some catalyst to the fuel, a couple of tanks full at least, and set off on a long burn with the engine working hard. If that makes no difference, and the blow by is worse, then your engine may have been overheated at some time or other and the rings lost a bit of tension. On the other hand, a Gardner in one of my friends' ex cray vessels was running very poorly, low on power, burning oil, and they expected it needed an overhaul, but catalyst and a Bass Strait Crossing under full load stopped it all and the engine then ran really well.

I would add NOTHING to the engine oil unless the engine manufacturer approves of it, and I would use only the currently recommended oil..
Yep, first thing to do if you suspect leaky rings and blowby, work the hell out of it with a long high throttle run.
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Old 31-07-2020, 08:33   #23
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Re: Yanmar 2GM20F - treatment for blowby

I don't believe that Marvel Mystery Oil is diesel with a aromatic. I have used it on auto engines and my Yanmar 3GM30F. When I used it in the engine of my Volvo Amazon, it cleaned the inside of the engine so well, I developed leaks in the front and rear crankshaft seals. So I think it really cleans well.

Lately, I have been using Seafoam in my Yanmar and the first time I added it to the diesel fuel, the engine started much quicker. I regularly add
Seafoam to the diesel and will also add a bit to my engine oil after the next oil change.
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