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Old 22-09-2010, 20:25   #1
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So Air Bubbles in the Fuel Line Are No Big Thing

I cleaned out the fuel tank, including removing the inspection port by which the primary intake pipe is plumbed. This (and cutting off the hose that attached to it) introduced what I thought would be a decent amount of air.

I filled the tank back up, and thought "well, I'll run the diesel till it dies from the air bubbles, then bleed out the bubbles and restart".

I started the engine, waited an hour, went sailing, motored back in later that night, never having even a slight hiccup. I have Racors and I watched the bubbles fly through the filters.

Diesel smart guys, what gives? Nigel Calder makes it seem like a single molecule of air will kill your engine.

Yanmar, 4JH.
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Old 22-09-2010, 20:42   #2
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The 4JH is among the Yanmars which essentially self-bleed. Some others are not that user-friendly
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Old 22-09-2010, 21:29   #3
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The 4JH is among the Yanmars which essentially self-bleed. Some others are not that user-friendly
What he said

Don't know about that particular engine....but I definitely have ones that are more cantankerous then others.

Depending on the rest of your plumbing and filtration set up the bubbles you see " Flying through your racor" arnt necessarily making it to the injector pump or injectors themselves...if they were you would definitely have hick ups....maybe not enough to stall your engine but make it stumble or loose power anyway.
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Old 22-09-2010, 21:31   #4
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You must have said a prayer to Saint Bleedius of Purgistan...the patron Saint of Diesel Engines.

Seriously, Racors can accept a small amount of air.....I have removed the tops of them and found the fuel level to be well below the filter element
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Old 22-09-2010, 21:32   #5
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Any engine that is "self bleeding" , in otherwords one that returns many times more fuel to the tank than it could ever hope to use will hardly notice air bubbles.
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Old 22-09-2010, 23:22   #6
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The 4JH is among the Yanmars which essentially self-bleed. Some others are not that user-friendly
Yep! The 3JH too! Here is a page out of the 4JH manual.


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Old 22-09-2010, 23:32   #7
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Yep! The 3JH too! Here is a page out of the 4JH manual.
Using a wrench By that term I suppose it's self-rebuilding too? I would think self-bleed means you do nothing but operate the pump. That's the way my Beta (Kubota) is. Or the earlier Universal (Kubota). I've never loosened any bleed screws. Not ever. Not on the filter or anywhere. Somebody solved the problem.
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Old 22-09-2010, 23:47   #8
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Using a wrench By that term I suppose it's self-rebuilding too? I would think self-bleed means you do nothing but operate the pump. That's the way my Beta (Kubota) is. Or the earlier Universal (Kubota). I've never loosened any bleed screws. Not ever. Not on the filter or anywhere. Somebody solved the problem.
It self bleeds out the small stuff while running, not a whole fuel line or filter. Read line #6 in the picture of my last post.
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Old 23-09-2010, 00:03   #9
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Any engine that is "self bleeding" , in otherwords one that returns many times more fuel to the tank than it could ever hope to use will hardly notice air bubbles.
Interesting. I've heard that the return line from the 4JH spits a ton of fuel back into the tank; I guess that's part of it.
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Old 23-09-2010, 02:30   #10
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Interesting. I've heard that the return line from the 4JH spits a ton of fuel back into the tank; I guess that's part of it.
I have the 4jh2-ute and yep, on our particular engine, the return is significant.
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Old 23-09-2010, 02:36   #11
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Yep! The 3JH too! Here is a page out of the 4JH manual.


.
Note there are several bleeding techniques for the 4JH series of engines depending on build date.
BTW I am interested in which engine and year was that from Demarrey
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Old 23-09-2010, 10:31   #12
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Note there are several bleeding techniques for the 4JH series of engines depending on build date.
BTW I am interested in which engine and year was that from Demarrey
I have a 2009 3JH4E.
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Old 23-09-2010, 13:11   #13
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I have a 2009 3JH4E.
Thanks for that.
Interesting its only a year later than mine with a very different bleeding system. The 4JH5 is different again.
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