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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance > Engines > Diesel
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Old 05-08-2011
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Another diesel bleeding question...

I have a Pearson 36 with a Yanmar 3GM30. I had to disconnect the fuel out/in lines at the tank in order to remove a lift muffler. I noticed that no diesel dripped out of the fuel lines when I disconnected them. The fuel lines are at the top of the tank, which made me wonder if the fuel just spills back into the tank when the engine is shut off. I've had people tell me I should still bleed the line, but then why didn't fuel drip out. Also their would be a lot of fuel to bleed in the 4-5' of fuel line between the tank and engine. Does air in the fuel line get replaced by fuel as soon as the engine is turned on, where maybe it's not necessary to bleed the system at that point?

Last edited by joelperez; 05-08-2011 at 12:33 AM.
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Old 05-08-2011
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the entire line won't be filled with air but it only takes a very small amount to cause the engine not to run,just try starting it,if it runs,fine no problem but normally a tiny bit of air will accumalate at the injectors so you will only need to bleed a small amount of fuel,yanmars are notorious for being hard to bleed but maybe you will luck out,btw no the fuel doesn't run back into the tank when the engine is shut off because the line/system can't draw air

Last edited by sawingknots; 05-08-2011 at 02:15 AM. Reason: more info
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Old 05-08-2011
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Good advice from SK, just don,t overcrank with a freshwater cooled system.
You can also bleed any air out by operating the manual lever on the fuel lift pump with the injector pump bleed open.
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Old 05-08-2011
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The fuel lines normally remain full of fuel. Air cannot get in the fuel line so the fuel cannot drain back even though the tank is lower.
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Old 05-08-2011
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I suspect that the fuel dripped back into the tank when you loosened the connections. You can certainly try running it without bleeding, but I don't think it will run long.
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Old 05-08-2011
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Aside from which, it never hurts to get in a bit of practice, so when you have to do it, you're ready for it.
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Old 05-08-2011
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As WS mentioned, since you've opened the system, the pick-up line within the tank will drain back to the level of the fuel in the tank. Whether your injection pump can 'purge' that amount of air on its own will depend on the design. Our Bosch is said to be 'self bleeding' and would probably be OK. Others may not like that bubble and need it physically bled. Of course this would only occur after restarting and actually pulling that bubble through the system and into the pump.

btw I've merged your two threads on this... please don't post the same question in multiple forums.
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Last edited by Faster; 05-08-2011 at 11:11 AM.
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Old 05-09-2011
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We're sort of back to the squeeze bulb . . . . . . I believe most Yanmars can be bled by just pumping fuel through the system. Mine (4JH3E) has never had the injector nuts loosened since I've owned it.
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Old 05-10-2011
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Thanks for all your comments.
It just seemed odd that their would be fuel at that point in the fuel line, since the tank has a vent, which wouldn't allow it to maintain a vacuum. Therefore, logically it would make sense that the fuel would just drip back into the tank when the engine is shut off. Because of the vent, the fuel in the line should just drop to whatever level the tank is at, like one of you suggested.
I'll bleed anyway. Betterr safe than sorry.
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Joe
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Old 05-10-2011
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Fuel lines on most diesels are generally designed to hold fuel against back-siphoning. Bleeding isn't difficult, though a bit messy.
If you have access to air, block your tank vent, regulate down to no more than 2psi air, and have an assistant pressurize you tank while you bleed.
If you have a check valve installed on the engine before the injector pump, you should only have to bleed to that point, then start the engine with the low psi air, then remove the air, and unblock the vent.
If no check valves in the system, then you'll have to bleed the lines at the injectors.
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