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Old 19-05-2014, 06:38   #1
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Yanmar Lift Pump Question

We finally got the old kitty off the dock yesterday for the first time in seven months. I'm still having air leakage issues with one of the 3HM35 Yanmars. After about 30-45 minutes running, it starts losing power and if I keep trying to run it will eventually stop within a minute or so of the first hiccup. I can immediately fix this temporarily by shutting it down and climbing down there and bleeding the top of the secondary fuel filter, and then the injector pump inlet. When tickling the yanmar's lift pump lever, I get bubbles out of the top of the filter etc.

Seems simple, but I can't find the source yet. I know that it must be on the suction side of the system i.e. between the tank and the output of the engine driven pump. But every bit of that has been replaced, twice in most cases. New Racor 500MA filter, new fuel line, new barbs, new hose clamps. All recently checked. Air intake leaks are hard to find, of course, since nothing is bubbling out, but I even had the local diesel shop do it the second time. To be fair, they couldn't run the engine at the time as it was on the hard.

But this tells me it must be someplace else? What else IS there?

Could this be a pump diaphram issue? Would that put air in the fuel line?
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Old 19-05-2014, 06:58   #2
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Re: Yanmar lift pump question

A restriction of the pick up tube can, mine did. God knows where it pulls air from, but if you block the suck side, the pump can apparently pull enough vacuum that it will get air from somewhere, or it may even be fuel vapor for all I know, but if you block the suck side once the restriction is removed, you will have to re-bleed the system.
If yours is partially blocked what you describe could happen.

I've only seen pump diaphragms leak fuel into the engine oil, but guess one could leak air.

Sounds like you have two engines? If so swap the pumps and see if the problem goes with the pump, I'm betting it won't.
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Old 19-05-2014, 07:05   #3
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Re: Yanmar lift pump question

I've seen pump diaphragms introduce air before, but it's obviously more common for them to either quit pumping or leak!

You've got 2 identical pumps... Why not swap them???

Another thought on looking for a leak the suction side of the feed.... Maybe pressurize the line and components with a few psi using an electric feed pump....
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Old 19-05-2014, 07:13   #4
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Re: Yanmar lift pump question

The local yanmar dealer/mechanic thought it was either a vent obstruction or clogged pickup tube, and that was one of the first things they checked. They pumped the tank out, in fact, and told me that it wasn't the problem, it was clean as a whistle.

In a rusted up bucket of old parts left on the boat, I found a little 12 vdc inline fuel pump from NAPA. I'm wondering if someone else had this issue. We had it all the way down from Florida, same symptoms.

Now I'm wondering if perhaps there isn't some kind of suction leak in the new Racor. I notice the paint has come loose from the top of it, unusual.

Scratching my head and looking for new places to find suction leaks now. I didn't think the pump diaphram was likely, but a maybe possibility. I'd think that it's constantly full of fuel so when it gets compressed by the cam it isn't sucking air, but is compressing diesel.

And when I use the lift pump to bleed the line it does it just fine. I think. It takes 20-30 pumps to get the bubbles out from the filter top. But then it's good for another half hour of cruise, or 45 min of idle before repeating the problem. Happens so often I leave both 10 and 12 mm open/box end wrenches right there.
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Old 19-05-2014, 07:48   #5
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Re: Yanmar lift pump question

Try running it from a jerry can or portable fuel tank to eliminate a tank/pickup tube problem. I had a similar issue that turned out to be a pin hole leak in the pick up tube. If the fuel level fell blow the hole, I started to get air in the line and engine stalling.
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Old 19-05-2014, 08:07   #6
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Re: Yanmar lift pump question

I had an air leak in a shut off valve once, took forever to find.
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Old 19-05-2014, 08:10   #7
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Re: Yanmar lift pump question

Quote:
Originally Posted by Capt.Alex View Post
Try running it from a jerry can or portable fuel tank to eliminate a tank/pickup tube problem. I had a similar issue that turned out to be a pin hole leak in the pick up tube. If the fuel level fell blow the hole, I started to get air in the line and engine stalling.

Good idea about the jerry can. That would let me check the system from the pump back, a junction at a time, until I find it. Gonna take a while, since I need to run it for a half hour or more with each change, but it would sure be worth it.

I don't think I have the same issues with pickup line. I don't have a vertical one. My tank is a big rectangle, above the level of the engine, and the fuel line is attached to a horizontal pipe located just slightly above the level floor of the tank. The fuel goes straight out the side of the bottom, through a valve, then into the Racor. From Racor to Pump.

Driving me nuts, trying to figure out where this air is coming from.

I can't imagine there is all that much suction. These little diesels only pull a half gallon an hour.
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Old 19-05-2014, 08:24   #8
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Re: Yanmar lift pump question

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Originally Posted by JusDreaming View Post
I had an air leak in a shut off valve once, took forever to find.
Now there's a thought! This valve is on a piece of threaded pipe sticking out of the side of the bottom of the fuel tank. It shuts off the fuel right at the source, and is the only valve left in the system.

I have a suction gauge on the top of my Racor. I would think that suction across the Racor, which is between that valve and the engine, would show up in the suction gauge, though.

Still, the valve looks like it's been there for all 28 years, and shouldn't be too hard to replace other than the tank has to be empty to do it. There's 25 gallons in that tank at the moment, but I could probably move that to the other tank temporarily.
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Old 19-05-2014, 08:31   #9
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Re: Yanmar lift pump question

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Originally Posted by JusDreaming View Post
I had an air leak in a shut off valve once, took forever to find.
Same here. For me it was the valve stem packing.
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Old 19-05-2014, 08:46   #10
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Talking Re: Yanmar lift pump question

Quote:
Originally Posted by a64pilot View Post
A restriction of the pick up tube can, mine did. God knows where it pulls air from, but if you block the suck side, the pump can apparently pull enough vacuum that it will get air from somewhere, or it may even be fuel vapor for all I know, but if you block the suck side once the restriction is removed, you will have to re-bleed the system.
If yours is partially blocked what you describe could happen.

I've only seen pump diaphragms leak fuel into the engine oil, but guess one could leak air.

Sounds like you have two engines? If so swap the pumps and see if the problem goes with the pump, I'm betting it won't.
That's a bit like swapping radio heads or efis screens but in this case it would open the fuel system on an engine with no problems. He will be returning to the gate with air in both fuel systems. I always got concerned when they did a brake change on hot days, both systems opened, never got all the air out. Just a matter of time till you get a " Hyd Temp Hi" Alert...somewhere inconvenient.
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Old 19-05-2014, 08:53   #11
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Re: Yanmar lift pump question

If it's any help, I install an outboard motor fuel squeeze bulb between the tank pickup and the fuel line leading into the primary filter (bank, I have a selector switch). It greatly speeds up the evacuation of air when changing filters and bleeding the line.
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Old 19-05-2014, 10:59   #12
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Re: Yanmar lift pump question

During the first week of our 40 day "delivery" sail to get this boat from Jax to Providenciales, I got so tired of flipping that little pump lever that I bought two squeeze bulbs in St. Augustine. I didn't think to check for diesel compatibility, come to think of it.

I installed one in each fuel line after the Racor. They worked great to bleed the line of air up to the injector pump.

Then when I had the local Yanmar dealer go through the boat and they changed all the fuel lines, they got rid of the squeeze bulbs. Told me that I didn't need them because my tanks are higher than the engines. Well, now I'm wishing I still had them. But diesel compatible.

I'll have to add a couple of them to my next importation order. Lets see, that's 150 ft. of chain, a case of SailKote, another Nature's Head, a seawater resistant version of a WorkMate if I can find one online......and three diesel compatible squeeze bulbs in 5/8" I think it is.
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Old 19-05-2014, 15:34   #13
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Re: Yanmar lift pump question

Which do you think is the more destructive, gasoline or diesel? I have never had an issue with these pumps using diesel.
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Old 19-05-2014, 16:08   #14
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Re: Yanmar lift pump question

I didn't have an issue with them, either. They worked great. I could crack that 10mm bleeder bolt while giving that bulb a squeeze or two and it was a done deal.

Yanmar dealer here removed them as part of a fuel line overhaul, trying to sort out this same problem. Obviously, it wasn't the squeeze bulb.

I would think gasoline is much harder on plastics than diesel. Especially when someone is stepping on it with ethanol. In fact I never heard of a different one for diesel til someone on here mentioned it.
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