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Old 23-08-2011, 16:34   #1
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Yanmar Lift Pump

I am having problems with my Yanmar lift pump. My engine is making oil. While in Mexico a couple of years ago I bypassed the lift pump and installed an electric pump. From Cabo to San Diego I had no problem with the engine making oil. When I returned to SD I replaced the lift pump and didn't have a problem -- till now. There were almost 7 quarts of oil in the sump when I did the oil change. I have brought a sample home with me and am going to have it analyzed but I am quite sure that there is diesel in the oil. Looking at the oil flow chart in the manual I see that the oil is used to lubricate the injection pump and thus has a source of putting fuel in the oil. Is there any way to install a Yanmar lift pump wrong and still have it work but leak diesel into the oil? Should I get permanently bypass the lift pump? Is there something in the injection pump that could be causing the problem?
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Old 23-08-2011, 19:38   #2
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Re: Yanmar Lift Pump

You would be hard pressed to install the lift pump wrong.

Is the electric pump feeding the lift pump?

If it is feeding the lift pump, you are probably forcing diesel fuel into the engine thru the seals in the lift pump.....I see this in a lot of boats where pwners DIY a way to fill their filters....instead of doing it the proper way.
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Old 23-08-2011, 19:52   #3
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Re: Yanmar Lift Pump

Charlie, the most likely cause is the lift pump but the high pressure pump could also be leaking diesel into the lub. oil.
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Old 23-08-2011, 21:00   #4
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Re: Yanmar Lift Pump

Quote:
Originally Posted by Chief Engineer View Post
You would be hard pressed to install the lift pump wrong.

Is the electric pump feeding the lift pump?

If it is feeding the lift pump, you are probably forcing diesel fuel into the engine thru the seals in the lift pump.....I see this in a lot of boats where pwners DIY a way to fill their filters....instead of doing it the proper way.
HI Chief I think I'm going to have to avail myself of your services. I did not hook the electric pump to the lift pump. I looped the line on the lift pump that went to the engine filter back to the suction end of the lift pump. I then plumbed in the electric fuel pump to the to the fuel filter on the engine. I figured that this was the way to not have the engine oil and the diesel have any point of contact. Was I correct? Is it "legal" for you to post how ones hires your services in this thread. If not could you please PM me and let me know how it works and if you feel that you could help me with this problem.

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Charlie, the most likely cause is the lift pump but the high pressure pump could also be leaking diesel into the lub. oil.
I am trying to find an exploded diagram of the HP Pump and the lift pump but I left my parts manual on the boat. I don't expect to be back there till next month so am taking this time to research the problem.
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Old 23-08-2011, 21:36   #5
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Re: Yanmar Lift Pump

If the Diaphragm on the lift pump is torn /leaking it could leak diesel into the block
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Old 23-08-2011, 21:42   #6
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Re: Yanmar Lift Pump

Thanks SC34 I'll check that next time I am down there.
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Old 23-08-2011, 22:01   #7
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Re: Yanmar Lift Pump

Hi Charlie, happened to me once, a nasty surprise and a crash course in Yanmar design. Sailorchic is right, a little tear, over time can let fuel in and overflow from the dipstick if fuel tank is higher. Try replacing once more, perhaps the one you installed is exchangeable?

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Old 24-08-2011, 07:41   #8
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Re: Yanmar Lift Pump

So your setup is like this....

Fuel tank>Primary Filter>Electric Pump>Secondary Filter>Injection Pump.

If so....something is blown in the IP
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Old 24-08-2011, 08:30   #9
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Re: Yanmar Lift Pump

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So your setup is like this....

Fuel tank>Primary Filter>Electric Pump>Secondary Filter>Injection Pump.

If so....something is blown in the IP
Chief right now it is set up like this fuel tank>Racor>Lift Pump>Secondary Filter>Injection Pump. If I set it up as you explained above then I don't get the creating oil problem.

I'll have to study the manual on removing the injection pump. Know I don't want to open up the pump but maybe removing it won't be that bad. Not sure how to find the oil leak.
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Old 24-08-2011, 12:26   #10
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Re: Yanmar Lift Pump

If the electric pump is not in the system, most likey you habe a failed diaphragm in the lift pump.

On gas engines there is usually a hose from the pump to the carburetor...in case the diaphragm goes, the fuel doesn't leak into the bilge or engine

Diesels don't have such a setup (Yanmar)
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Old 24-08-2011, 13:26   #11
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Re: Yanmar Lift Pump

I will pull the lift pump and run the test that is recommended in the repair manual. If the diaphragm is bad then I believe that I can replace it. What I am confused about is why two of them would go out in such a short period of time. The engine has less then 600 hours on it?
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Old 24-08-2011, 14:31   #12
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Re: Yanmar Lift Pump

They can fail if they are trying to pull too much of a vacuum.

This could be due to a severely clogged filter or obstruction in the fuel feed from the tank
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Old 24-08-2011, 14:53   #13
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Re: Yanmar Lift Pump

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They can fail if they are trying to pull too much of a vacuum.

This could be due to a severely clogged filter or obstruction in the fuel feed from the tank
I have a dual Racor with a pressure gauge on it. With this i will be able to tell whether or not there is excessive pressure. Correct. Does this need to be under load or can it be at idle with high RPM at the dock.
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Old 24-08-2011, 18:54   #14
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Re: Yanmar Lift Pump

You mean a vacuum gauge?
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Old 24-08-2011, 22:28   #15
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Re: Yanmar Lift Pump

Racor 2666790 MAX-DUAL Fuel Filter/Water Separator is what I have.
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