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Old 02-08-2023, 14:02   #1
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Diaphragm Lift Pump Life

I have a Yanmar 4JH3E that is 22 years old with 3600 hours on it. Last month for the first time ever I got an oil analysis on it and everything looked good except there was 2% fuel in it. Maybe nothing except that have lately only been running engine at no load while in marina, may be fuel injector but don't have any smoke, and it may the lift pump leaking.

Since the engine is pretty old with a fair number of hours I wonder if I should just replace the lift pump. An aftermarket one is only $34 and it may be worth rebuilding the OEM. Then again maybe should just replace it with an electric pump.

Who has had their lift pump fail and how many hours did the engine have?
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Old 02-08-2023, 14:25   #2
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Re: Diaphragm Lift Pump Life

The diaphragm on my Volvo MD17 failed after about 22 years and an unknown number of hours. The problem manifested itself by dumping rather a lot of diesel into the bilge.
I would suggest changing it.
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Old 02-08-2023, 15:57   #3
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Re: Diaphragm Lift Pump Life

The path of least resistance is to replace the lift pump, itís earned its keep after 3,600 hrs ....and you might be right about no load running but Iíd expect to see a light sheen on the water around the exhaust outlet. Another possibility and a fairly remote one on your engine is that the injector pump plungers are leaking. On some engines this is relatively normal, changing the lube oil in a Ford Lehman pump often shows almost pure diesel fuel in the cambox when the drain plug is opened, Bosch and Simms pumps had an actual external case drain pipe that sometimes dripped fuel into a catch can (or the bilge)
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Old 02-08-2023, 16:39   #4
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Re: Diaphragm Lift Pump Life

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Originally Posted by skipperpete View Post
The path of least resistance is to replace the lift pump, itís earned its keep after 3,600 hrs ....and you might be right about no load running but Iíd expect to see a light sheen on the water around the exhaust outlet. Another possibility and a fairly remote one on your engine is that the injector pump plungers are leaking. On some engines this is relatively normal, changing the lube oil in a Ford Lehman pump often shows almost pure diesel fuel in the cambox when the drain plug is opened, Bosch and Simms pumps had an actual external case drain pipe that sometimes dripped fuel into a catch can (or the bilge)

SkipperPete-
are you saying that some sheen on the water while running is fuel in the exhaust (and is that due to the lift pump?). I have a 4jH3-TE and have a wee bit of smoke and some sheen.
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Old 02-08-2023, 17:25   #5
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Re: Diaphragm Lift Pump Life

Yes, it usually is UNLESS your engine uses a lot of oil. Iím often surprised by how long unburnt fuel can linger in an aqualock after doing a longish period of cranking trying to start a difficult engine, it could be as little as a total of 30 seconds total cranking over an hour but that raw fuel takes the easy path to the exhaust, not to the sump past the rings. Remember that most injector pumps go to max fuel after shutdown so thereís plenty squirting into the engine at cranking speed. Most engines flash up quite quickly, around 2 or 3 seconds for a sluggish start so pretty dry in the cylinder.
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Old 02-08-2023, 18:23   #6
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Re: Diaphragm Lift Pump Life

I never have a sheen
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Old 02-08-2023, 18:59   #7
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Re: Diaphragm Lift Pump Life

This is the sort of thing that made me decide to stop getting oil analysis done.


My boat's engine is 25 years old, 2800 hours, and I have no idea if the lift pump has been replaced.


I had four diesel tractors and a skid loader over the years and never replaced a lift pump. Of the five engines, three were over 10,000 hours when I sold them, one was at 3,000 hours, and the other is at around 30 years old and 800 hours. My advice is to change the oil and filters etc per the maintenance schedule and leave everything else alone unless it breaks.


I guess there's also a lawn mower/snowblower with a Yanmar diesel that my Mom has that has maybe 1000 hours on it, 10 years old or less, no repairs to the engine ever.
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Old 02-08-2023, 19:09   #8
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Re: Diaphragm Lift Pump Life

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Originally Posted by skipperpete View Post
Yes, it usually is UNLESS your engine uses a lot of oil. I’m often surprised by how long unburnt fuel can linger in an aqualock after doing a longish period of cranking trying to start a difficult engine, it could be as little as a total of 30 seconds total cranking over an hour but that raw fuel takes the easy path to the exhaust, not to the sump past the rings. Remember that most injector pumps go to max fuel after shutdown so there’s plenty squirting into the engine at cranking speed. Most engines flash up quite quickly, around 2 or 3 seconds for a sluggish start so pretty dry in the cylinder.
My engine oozes a bit but not a lot of oil. It has 5000 hours. Will research what replacing that would cost. Oh and it starts when I wave my hand over the start button. Always has!
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Old 02-08-2023, 19:17   #9
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Re: Diaphragm Lift Pump Life

Quote:
Originally Posted by Jammer View Post
This is the sort of thing that made me decide to stop getting oil analysis done.


My boat's engine is 25 years old, 2800 hours, and I have no idea if the lift pump has been replaced.


I had four diesel tractors and a skid loader over the years and never replaced a lift pump. Of the five engines, three were over 10,000 hours when I sold them, one was at 3,000 hours, and the other is at around 30 years old and 800 hours. My advice is to change the oil and filters etc per the maintenance schedule and leave everything else alone unless it breaks.


I guess there's also a lawn mower/snowblower with a Yanmar diesel that my Mom has that has maybe 1000 hours on it, 10 years old or less, no repairs to the engine ever.

Got a couple of 40 year old Yanmar lift pumps (unknown hours), they are still working.

Got a 56 year old lift pump on a diesel tractor (with unknown hours but greater than 5,000 when the hour meter stopped working years ago) and it is still fine.

Mind you, I hope this post hasn't put the kibosh on them.
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Old 02-08-2023, 19:30   #10
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Re: Diaphragm Lift Pump Life

I believe in replacing stuff before it breaks, when it nears the end of its expected life.


Twenty years is a reasonable interval for replacing a lift pump. They are not expensive. And it will ruin your day if you wait until it fails before you replace it.


I had a fuel pump fail on my Yanmar 3GM30 a few months ago, after 22 years. I was a little lazy. Because the tank is higher than the pump, the sure sign was that the diesel would only run about 1,500 rpm.


That apparently was how quickly diesel would flow downhill into the lift pump. I installed a new pump in half an hour or so. Problem solved. The next owner will have to deal with it again in another 20 years.
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Old 03-08-2023, 00:58   #11
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Re: Diaphragm Lift Pump Life

I reckon that a boat engine is more mission critical than a tractor engine and requires a higher level of preventative maintenance. On the fuel system subject , many tractor engines are fed from a tank either above or at the same height as the engine, this is not always the case with boat fuel systems where the lift pump has a harder job pulling fuel from keel tanks or wherever the engine is higher than the tanks.
If a tractor gets a sump full of diesel it means a quick oil change and a trip to town for a drum of lube oil, on a cruising yacht there may not be enough room to carry a drum of oil or even time to do the drain and fill in a seaway or while navigating in difficult circumstances. Far better to replace the humble lift pump early, it might be the best 40 dollars you ever spent.
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Old 03-08-2023, 04:27   #12
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Re: Diaphragm Lift Pump Life

A search on CF comes up with threads of failed lift pumps with way less hours than mine that filled the oil with fuel.

I will think about it, but think it probably worth at least having the pump around as a spare.

Am thinking the same for the water pump since that is only $105.
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Old 03-08-2023, 05:25   #13
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Re: Diaphragm Lift Pump Life

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I believe in replacing stuff before it breaks, when it nears the end of its expected life.

Twenty years is a reasonable interval for replacing a lift pump.

Why the lift pump in particular? Where do you stop? 20 years is a long time for the main seals too.
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Old 04-08-2023, 06:14   #14
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Re: Diaphragm Lift Pump Life

Most small diesel mechanical lift pumps are designed for tractor or generator applications that are designed to operate with very little lift and a short distance from the tank. Many tractors have the fuel tank above the lift pump so there is no lift at all. IF your vessel has fuel tanks well below the engine or far from the engine, you are asking the little lift pump to operate in a manner that it was not designed. Expect a shorter life expectancy from the diaphragm and less fuel flow. Fuel flow is important as even if the fuel is not burned, the excess fuel is intended to cool the fuel pump and injectors as it returns to the tank.
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Old 04-08-2023, 16:14   #15
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Re: Diaphragm Lift Pump Life

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Why the lift pump in particular? Where do you stop? 20 years is a long time for the main seals too.


Thatís an excellent question Jammer, mechanics are confronted with this dilemma regularly and often refer to the time honored ď If a 90 year old man gets a hip replacement or an organ transplant does that make him young again?Ē And the answer is always no...... and the same answer should apply to engines. A top overhaul and a set of bearing shells is not a zero hours overhaul, you still have the old oil pump: the same conrods : bolts: timing gears: camshaft: crankshaft and of course , the engine block. The early fail items are easy to identify and replace, Vee belts, anodes, mixer elbows, coolant hoses , filters, raw water pumps and impellers are some of the obvious ones but thereís a second layer or level that includes circulating pumps drive plates and lift pumps... the stuff that lives for year after year and finally snuffs it at the most inconvenient time.... but could have easily been replaced earlier.
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