Bleeding problems on a Yanmar diesel engine - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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  #1  
Old 09-08-2009
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Question Bleeding problems on a Yanmar diesel engine

I am have been trying to bleed the fuel lines for a Yanmar diesel engine (model 30GM30F) for 3 days now...How many manual pumps does it take to get fuel coming out of the fuel pump bleeding screw??????

A bit of recent history:

I changed the primary filter (Racor) and then primed it by toping it off with fuel.

I changed the secondary fuel pump filter (but did not fill it with fuel, as I just read earlier in another thread).

The first time I used the manual lever on the lift pump I did not know what kind of "pressure" I was supposed to feel, but nothing (no air bubbles nor fuel) was coming out of the bleeding screws. I had not read at that point that I should turn the engine a half turn (by manually moving the belt) in order for the pump to have pressure and be able to actually pump. So, to see if the lift pump was working, I disconnected both the intake and the outtake hoses (of course letting yet more air into the fuel lines, I now realize).

So, once I realized the error of my ways, I made sure all connections were back on and secure and started pumping while cracking the fuel pump bleeding screw. After quite awhile pumping I did get air bubbles, then nothing, then more air bubbles, then nothing. I did the same thing with the bleeding screw on the fuel injector pump and got the same results. However, I have not been able to get fuel flowing without air bubbles as I read I should. The first time I bleed the screws I did have fuel with bubbles but now I see only air bubbles or nothing. At one point the fuel intake handle coming in from the fuel tank was closed off, but I reopened it and have pumped for a long time.

My patience is really running thin. How much do I need to keep pumping? Is the lift pump no longer working though I feel pressure on it? If I disconnect all the fuel lines to make sure there is no blockage then how in the world will I bleed that much air out?

I'd love to hear from anyone with some suggestions.
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Old 09-08-2009
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Since I have made this mistake myself, it's worth asking!

Did you turn the fuel tank / supply valve back on (if you turned it off to do the work)?
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Old 09-08-2009
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As it so happens Northeaster, I THOUGHT that the fuel tank supply valve was back on. However, I discovered that the valve has a 180 degree rotation rather than just a 90 degree one. So when I supposedly turned it back on, it was in the wrong direction. My father (83 years of age and the boat owner whom I'm trying to help out) noticed that the "pointer" was facing the wrong direction. I rotated the valve and bingo, fuel flowed through and I was able to do the bleeding just like it's described in the books. The engine started up and ran fine. Thanks for the tip. This sure is learning by error!
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Old 09-09-2009
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Good to hear it worked out! I know that when I did the same thing, I did get a few bubbles as well, and was confused, until I finally thought of the valve.

Take care!
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Old 09-12-2009
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I have a Volvo Penta engine but all your trials and symptoms sound almost identical to what I have experienced since spring. I replaced the fuel lines last winter and had trouble getting it started after I thought I had done a good job of bleeding the air out. I talked to the mechanic at the marina and he offerred a simple solution that worked very well. He told me to get a simple outboard motor type squeeze priming bulb (Moeller makes them and they sell for about $10). He said the mechanical pumps don't have the pressure to force the fuel and bubbles etc. through the lines. I got one and it works great. My problem was that I had a second problem that it took me a while to find. The banjo fitting on the inlet to my fuel pump was missing a washer on one side and was sucking in air, causing the engine to either not start or stop running. This was getting worse over the summer till I finally drained and pressure tested all the lines and found the missing washer. Each time it happened the squeeze bulb made it possible to bleed the system and have the engine running again in 10 to 15 minutes (was still a real pain).
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Old 09-13-2009
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Thanks harbin2 for the suggestion; I'll keep it in mind.
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Old 09-14-2009
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There have been other threads on squeeze bulbs, here, and on other forums.

Many agree thye make bleeding easier. Personally, I find the mechanical pump works fine, but I have great access to it, unile on some boats, where reaching / operating it is a pain.

Beware that you may fail an insurance survey, as the squeeze bulbs are not approved for use below decks, as they are meant for outboards, etc. I am not an authority on this, but thought you may want to know this, before adding one.
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Old 09-17-2009
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Thanks Northeaster for the insurance comment.
My pump lever is fairly accessible but it doesn't seem very effective - even when I rotate the engine so it works. But there were a couple things I was skeptical about in using the bulb (which does work very well) and was thinking about removing it now that I've solved my air inleakage.
1. I'm sure it offers a little resistance to fuel flow but not sure if it makes much difference.
2. I have been a little nervous about over pressurizing the system using the bulb. I usually end up squeezing it pretty hard but it doesn't seem to have had any detremental effects on the fuel pump diaphragm or anything else in the system.
Any thoughts?
Thanks again.

harbin2
Islander 30 Bahama, 1981
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Old 09-17-2009
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Let me begin by saying I am no expert here - have just gotten to know my boat, and Yanmar 2GM really well!

I doubt you would have an issue with either flow or overpressurizing from the squeezebulb. The greater chance of trouble would come from the often inferior clamps / fitting possibly aloowing air leaks in, or fuel leaks out. Air leaks could hurt performance, and reliablility. Possible fuel leaks could cause fire / insurance problems.

Re: the mechanical pump not working well. Iam more used to gas engines than diesel, but being a four stroke, I am guessing that the camshaft may only allow the fuel pump to work well from the lever, in one or 2 of the 4 possible strokes (someone feel free to correct me). What I mean by this is if the pump doesn't seem to be working well, using the lever, flip the decpompression levers, and crank teh engine over once. If it still doesn't work, try it again, and possibly again, until you feel more resistance, in the last part of the pump stroke. hopefully you should see fuel coing out the bleed hole ASAP.
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Old 11-14-2009
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I see it's been awhile. In case anyone looks at this again. I put two three way automotive gas valves, You old guys should remember these from the old Ford truck days with the tank behind the seat and the other underneath the cab, around $30 apiece and an 12V electric fuel pump $55, inline with the fuel tank outlet. This pump puts out 8lbs. of pressure and has a lift of 24". It is set up to use whenever I do a filter change. Pure pressure no air all the way to the secondary filter bleeder screw. When done just turn it back to straight flow. This is really good when you are frustrated bleeding the system, you always have pressure to the engine.
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