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Discussion Starter · #1 ·
I was motorsailing, turning about 2000 RPM on a Yanmar3GM30. Suddenly, the engine lost power. It wasn't exactly missing but it wasn't delivering power. I shut down and restarted but with the same symptoms and then wouldn't run at all. A few days later, it started right up and ran with no problem. The same thing had happened a earlier, maybe 50-75 motor hours earlier. Any thoughts?
 

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Bombay Explorer 44
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Check for fuel supply restrictions. Partially blocked filter being the most obvious. Kinked or flattened hoses are another possibility.

The old 'rag in the tank' will do it as well.
 

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If your not already using a 'biocide' in your fuel, and the filters are not plugged, look for obstructions 'growing' in the fuel system such as 'fibrous mats' of growing funguses and bacteria colonies ... dont forget to inspect the tank's dip tube and the 'silly small' inlet screen on the inlet of the tank's dip tube.
The only way to clean out such 'mats', etc. is to push a wire through the tubing, and then consider to fully clean out the tank, followed by a massive dose of a bio-cide.
 

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Sailor
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Most likely clogged filters. Change and then re-bleed. Check the filters; how dirty are they? How long since the last change? If recent, your tank is dirty and you should consider fuel polishing to clean your fuel.

Tod
 

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Discussion Starter · #8 ·
When the incidents occurred, the Racor (2 micron) had less than 100 hrs and was nearly pristine. I had the fuel polished, but the technician said that it was as clean as could be and that the tank was free from dirt. He said, "I don't know what you are doing, but keep it up."
 

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Whoa! Something is wrong/amiss here.

"A few days later, it started right up and ran with no problem" .... pretty much "THE" symptom of a bio-mass etc. 'plug' somewhere in the delivery tubing or tanks 'dip tube'. The plug moves, extrudes due to the high 'vacuum/pressure' against it, the engine starves for fuel and shuts down, and then the plug 'self-releives' the blockage ... but 'just enough' to equilibrate the pressure/vacuum back to 'zero'; but, still there and ready to re-block the system when fuel flow again starts. The (fibrous) bio mass plug is acting like a 'filter', a filter of extremely small surface area and a filter that is 'totally plugging' and then slowly relieving itself when there is no vacuum/pressure applied against it.

My bets remains on a biomass blockage somewhere in the delivery line ... probably between the 'first filter' and the liquid in the tank.

If you dont have a biomass plug somewhere in the tubing between the tank and your 'filters' or the inlet screen on the tank dip tube is not blocked, I would strongly consider to 'bet the farm' that your OEM spec. engine fuel/particle requirements are for a 15-18µM engine mounted 'guard' filter ..... not a 2µM.

That 15-18µM engine 'guard filter' should be preceded with a 10µM Racor type (and that 10µM preceded with a 30µM if the historical system filter performance requires constant and premature and early filter changeout due to visible particulate !!!!!!). Yanmars, Westerbekes, etc. all have this 20µM spec. and will have an 15-18µM 'guard' filter engine mounted by the engine manufacturer on the engine.

The simple reasons for a 2µM to plug so easily, and no matter what the 'surface' of the 2µM looks like, is that
1. when there is widespread particle contamination, the smaller the particle the exponentially more of them will be in the fluid. Its the particles that get trapped INSIDE the filter media (pores) that do the 'blocking' of the flow, much less than what appears to be on the 'surface' !!!!!
2. It takes work (pressure drop) to operate a filter. A brand new 2µM will have 5X the flow resistance of a brand new 10µM filter (of the same filter material and the same surface area size). This also means that the internal velocity of oil inside the 2µM filter material is traveling 5X faster than a 10µM ( of the same exact filter 'surface area') ... the result is MUCH 'deeper' penetration of particles into the filter media with a 2µM than a 10µM. This increase of internal velocity through the filter material will result in less on stream life (to plugging) by a factor of about 10 times 'faster' to plugging.
If your basic engine spec. is for 20µM (98% of all marine diesel engine are) and you havea 2µM in place of the 20µM (10µM in actual practice) then you really have to increase the surface area of that 2µM by at least 5 TIMES to get the same on stream filter life and same flow rate per pressure drop (Q/∆P or gallons per hour PER psi drop across the filter) out of the 2.

Typical Filtration: Tank --> 30µM prefilter (optional) --->10µM (main filter) ---> 15-18µM small surface area engine mounted 'guard' (or 'last chance' filter) --> engine.

Offered solution:
Validate that the tubing between the 'first' filter in the series and validate that the delivery tubing from the tank and/or the tank dip tube or its inlet 'screen' isnt plugged ... disconnect the inlet side of the 'first' filter, take a small bicycle type air compressor/pump and attempt to blow the lines clear - back to the tank. IF the lines are 'clear', then concentrate on that 2µM filter ... which for 98% of all small marine engine applications should be a 10µM.

Suggest that you put a vacuum gage on that 'first' filter housing so you can monitor the build up of 'vacuum' when the filter begins to 'plug' and no longer can deliver the amount of fuel at that vacuum/pressure. With the gage installed, when next time the engine begins to 'stumble' when at cruising rpm or higher quickly note the vacuum reading on that gage. Multiply that gage reading by .8 and that the 'vacuum' reading (times .8) will now be your future 'change-out-the-filters' pressure/vacuum reading, leaving you 20% of reserve flow capacity ... to get home with.

VISUALLY TEST THE PRESNT FUEL --->
Remove some fuel from the tank. Put it into a clear glass container (an old drinking glass, etc.), hold the oil filled glass between your eyeball and VERY STRONG white (or Sun) light. If there is ANY cloudiness or any noted HAZE in that oil, you HAVE a massive amount of particles at greater than about 2-5µM in that oil ... and the tank should be thoroughly cleaned, and then the oil recirculation polished (again?) until 'clear'.
If Haze and if you have an oil burner at home, remove the oil from the boat, take it home and put in the oil burner tank, and then buy your diesel oil only from a 'truck stop' or a high-turnover marine fuel depot that caters to commercial boats and 'watermen'. Uncontaminated fuel (particles at less than 1-2µM) will have essentially NO haze when examined by the above 'water glass + light' test.

What is the engine mfg. and its FULL model number?
 

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Discussion Starter · #14 ·
The engine has had hundreds of hours on a 2 micron filter with no problems ever. I have changed the Racor religiously. The tank was clean and the fuel clean. I have nearly always had a problem bleeding the system after a filter change. I am beginning to believe that the problem was due to a fitting , either at the lift pump or at the injectors, leaking air.

I do appreciate all the advice, but I do not believe the problem has anything to do with clogged filters, obstructions in the fuel lines or water in the fuel. I have owned this boat for many years and motored more than any sailor would care for. aa3jy has the most intriguing thoughts on the problem. I will check all fuel line connex for the possibility of air intrusion. At any rate, keep the ideas coming
 

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As the years go by, it's very commin for sludge to build in the tank. Past experience is not an indication of future performance of either the stock market nor a fuel system. I wouldn't dismiss the filtration issue so readily, based on the past.

Hope you figure it out.
 

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The engine has had hundreds of hours on a 2 micron filter with no problems ever. I have changed the Racor religiously. The tank was clean and the fuel clean. I have nearly always had a problem bleeding the system after a filter change. I am beginning to believe that the problem was due to a fitting , either at the lift pump or at the injectors, leaking air.

I do appreciate all the advice, but I do not believe the problem has anything to do with clogged filters, obstructions in the fuel lines or water in the fuel. I have owned this boat for many years and motored more than any sailor would care for. aa3jy has the most intriguing thoughts on the problem. I will check all fuel line connex for the possibility of air intrusion. At any rate, keep the ideas coming
Sure, quite possible its an air leak at one of the fittings as boat builder continue to use the cheapest of the cheap 'compression fittings' in fuel lines. The problem with such is that the compressed copper 'relaxes' after long term stress which allows that little ferrule to no longer seal. Also such fittings by design are one time close ... and 'should' have the end of that copper tube trimmed back each and every time you open such a fitting. Compression fitting are notorious air/gas leakers.
However, if any fitting, filter gasket, filter O-ring was leaking air ... you'd wouldnt be able to start the engine after several hours of sitting as there would still be air in the fuel line. Soooooo and without physically examining, my 'bet the farm' guess remains with a bio-mass plugged fuel line or dip tube .... or even a blocked tank vent or vent line. A filter mounted vac. gage would tend to confirm the need to check that fuel line and dip tube.

;-)
 

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Corsair 24
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its always the simplest either an air leak or too much slowing down of the fuel flow

this could by sludge, buildup, too much filtering etc
 
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