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Old 02-11-2012, 03:58   #1
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Dieselpest - How To Avoid It?

Dieselpest is caused by microorganisms multiplying in the presence of water. I know all that. Here in Denmark, old, water-logged diesel is generally not a problem, but I pour a half liter of carburetor alcohol in my tank every time I fill it. Never had any kind of problem.

Planning to go blue water. I suspect that the diesel you buy in out of the way places quite likely will be candidates for 1st prize in the water-logged category


What do you do to avoid the pest?

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Old 02-11-2012, 12:11   #2
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Re: Dieselpest - How To Avoid It?

The easiest, and most expensive option is a fuel polishing system. Next would be a constant fuel filtering system with a fuel/water separator.

A true fuel polisher requires pretty fast throughput (the recomendation is for the entire tank an hour), and may not be practical. But a filtration system, that is just a few filer media and a separator with a moderate sized fuel pump is pretty easy to home build, and can save a lot of problems. Both with wet fuel, and with gunk.

Frankly these days what I see more of isn't growth in the tanks, but fuel that is starting to seperate. This is a function of the way diesel is made, where they crack large molecules into smaller ones with enzymes. The problem is as the enzymes evaporate the molecules reform into tar. But whatever the source of the crud in your tanks a filtration system will remove it.
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Old 02-11-2012, 12:26   #3
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Re: Dieselpest - How To Avoid It?

If the source of the diesel is suspected of water or contamination then filter it before it goes into your tank.

The old Baja filter which is no longer made or the funnel filter from West Marine. The West Marine filter tested very well in keeping water and crude from entering your tank.
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Old 02-11-2012, 12:53   #4
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Re: Dieselpest - How To Avoid It?

Yeah, my thoughts were obviously to filter before filling. Filtering does necessarily get the water out. Ideas?
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Old 02-11-2012, 12:55   #5
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Re: Dieselpest - How To Avoid It?

Yes, the West Marine funnel filter does indeed filter water and keep it out of the tank.

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Old 02-11-2012, 13:13   #6
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Re: Dieselpest - How To Avoid It?

Thanks for the tip. Just looked at it
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Old 02-11-2012, 13:23   #7
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Re: Dieselpest - How To Avoid It?

Look, diesel fuel is hydroscopic, so will absorb water from the air in any case. It will become saturated, then give up some of that wAter when the temp goes down, to settle out in the bottom. There'really nothing you can do about it besides cleaning out your tank on a regular basis - for me, every three years.
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Old 02-11-2012, 13:26   #8
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Re: Dieselpest - How To Avoid It?

Prefilter as suggested (Baja Filters are very effective)

Full tanks = less condensation.

Add biocide like BioBor brand.

Good oversized filtration system for when all the above does not get it all. For example, my engines use less than 1 GPH at cruising RPM, but my filtration system is rated for 65 GPH -- it can handle a lot of gunk and still move 1 GPH. I've removed some very dirty filters from it in the past, but never had an engine fail due to a fully clogged filter.
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Old 02-11-2012, 14:16   #9
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Re: Dieselpest - How To Avoid It?

Diesel is not hygroscopic. It gets water in it because the air in the tank condenses water out that settles in the bottom of the tank. The other sources are leaks in fuel lines and water logged diesel to begin with. That mostly would only happen if you take on diesel from the bottom of the tank, however. Much more likely to get contaminated diesel from the bugs and or grow them in your tank. Biobor or other bacteriacides will keep the bugs at bay. Racor 500 filter will handle most of the bugs that are already in the fuel. Riggine two filters in parallel so you can switch out one filter while running off the other will pretty much keep you going forever.
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Old 02-11-2012, 15:05   #10
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Re: Dieselpest - How To Avoid It?

Check the gasket on your fuel filler cap, and replace if necessary.
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Old 02-11-2012, 16:02   #11
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Re: Dieselpest - How To Avoid It?

Part empty tanks will always draw in water--because of temperature differences and the latent heat of evaporation of water, which combines to pump water into the tank over a long period of time--just as it pumps water into PVC aerial cables which run uphill. The water collects in the topmost terminal. Day/night temperature fluctuations reduce volumes and allow the ingress of evening moisture laden air--which then condenses on the metal tank walls and sinks to the bottom of the main fuel tank, where the diesel fuel covers it and makes it less likely to evaporate again come morning. Enough of the why fore--what to do about it?

Firstly--make sure you purchase only clean fuel.

My tanks are circulated continuously when the engine is running, and a header tank with constant flow pump through a pair of large filters does this bit--keeping the header tank full and putting the filtered fuel back into the top of the main tank where it is slightly warmer than the rest of the fuel--and the pump draws from the bottom of the main tank where the previously filtered fuel is colder. The next ploy is to fill all main tanks before leaving the vessel, and to make sure the tanks air-inlet system is separate from the filler cap and properly water proof. Mine goes through a stainless steel wool filter (easily made by my good self which stops wildlife getting in and also serves as a flame excluder as well. behind this is a carbon canister filter--as used in any automotive fume collecting device.

The next ploy is to use a biocide if you are not using the vessel over winter or for any extended period of time. There are several brand products available which seem to work OK. Cleaning out a badly contaminated tank is a bastard of a job, using heat or strong disinfectants and steam cleaning--followed by a thorough drying using hot dry air which usually means the tanks have to come out. Much better to prevent problems in the first place.
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