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Old 10-25-2015, 12:11 PM   #21
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The old high sulfur and no bio would last decades. However most diesel today is low sulfur and does not last as long. The length of time depends on your location and if your main engine, gen set and diesel heat polish the fuel, or if you polish the fuel. Most diesel engine draw more fuel than the use, so do heaters. So the polish the fuel while the run. Our, main 671 draws 50+gallon but use max 5 gph. Thus 40 gallons are returned to the tank clean polished. Most large fuel tank long range boats have fuel polish systems. So we can sit at the dock and polish the fuel.

Its water moisture in the tank and the fuel separating out out that is the cause of algae bugs. So I add additives that absorb the water moisture back in the fuel and the additve wil
Prevent separating, tarring. So if depends on you boat, area, and prevent mrasures you use.

If you are concerned might want to have double filters, so it a filter is bad, you can switch over to a new filter and replace the old while the engine is running. Best to have vacuum gauges on the filter so you can monitor the fuel filters.
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Old 10-25-2015, 02:23 PM   #22
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Interesting discussion, I appreciate all the input. One thing I neglected to mention is that this winter (she was just hauled) I am replacing the original fuel tanks.

I think after listening to everyone's comments I will have the fuel professionally polished (assuming the cost is not crazy) and then pump it back into my shiny new fuel tanks and use it next summer.
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Old 10-25-2015, 02:42 PM   #23
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Well, I woke up this morning to an email from my petro engineer friend (he is in Indonesia so he must have had a boring work day to send all of it to me) explaining what the little microbes do and their effect on diesel. He even included a PHD Thesis he found by some guy at Texas Tech explaining the whole process, most of which I am not capable of understanding. But a summary of what he explained to me:

The microbes are naturally occurring bacteria that feed on the carbon in the diesel hydrocarbon molecule. They consume the carbon, using relatively vast (for them) amounts of oxygen, thus breaking up the diesel hydrocarbon molecule and leaving hydrogen behind which will either evaporate or combine with the oxygen to make water. Apparently, this is a very slow process. These bacteria have been used to clean up oil leeched into the soil in spills, but because it is slow, it is not all that effective. The long and short of it is that the bacteria are eating your fuel! If left long enough, they will consume all the available carbon, become a huge soggy organic mess, and die off and you have a ruined tank and no fuel. That said, that would take a very, very long time. This is a naturally occurring process that begins as soon as fuel leaves the refinery. Hence the need for fuel filters. His opinion finally was that fuel treated with a biocide and filtered (polished) regularly would essentially last forever although whatever growth there may be between filterings will be eating away very tiny, tiny amounts of your fuel volume. There is nothing in the chemistry of diesel fuel itself that causes it to "degrade" losing its ability to ignite and combust. According to him the hydrocarbon bond in diesel is one of the stronger chemical bonds (which explains big refineries!). Hope most of this makes more sense to some of you than to me.
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Old 10-25-2015, 03:58 PM   #24
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It might be worth considering sending a sample of the fuel to an oil testing lab. Many labs also test fuel for contamination. For ~$40 it would be worth it with the fuel quantity you have.

Lehmans, to my knowledge, do NOT pump a large quantity of fuel beyond what they use. There is some excess but unlike some engines there is not a lot of return fuel so the engine itself is not terribly effective as a polisher.

For confirmation one way or the other try contacting American Diesel who are the gurus of these engines.

American Diesel Corp
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Old 10-25-2015, 05:12 PM   #25
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When you buy fuel at the dock, do you know how long it's been in the storage tanks for? Middle of the season it may be fresh but early season, who knows?
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Old 10-25-2015, 05:29 PM   #26
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Quote:
Originally Posted by Ski in NC View Post
I too have been "donated" old diesel fuel from folks that consider it "too old" to use. I mix it with new, maybe 50/50, then use it in my machines. Never had a problem. Some was over ten years old.
Me too, gas, diesel and kerosene.

Any of you Northern California members looking to donate old fuel just shoot me a PM.
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Old 10-25-2015, 06:32 PM   #27
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Fuel polishing on the simple. Get either a Gulf Coast Filter or a Racor and add a Walbro FRB-13 pump to pull the fuel through the filter. Add a couple of ball valves and hose tees so you can draw fuel from before the primary filter and return it after the engine. You can then when at rest draw the fuel from the tank pull it through the filter and then back to the tank. Underway you close the ball values and the polishing system is not interfering with your fuel system.
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Old 10-25-2015, 06:43 PM   #28
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Quote:
Originally Posted by Destiny View Post
When you buy fuel at the dock, do you know how long it's been in the storage tanks for? Middle of the season it may be fresh but early season, who knows?

It's simple. The fuel in the tanks is at most 6 months old. The fuel being discussed here is anywhere from a year to several years old.

The inground tanks stay relatively cool which inhibits the bio growth. There's a big difference between shoreside fuel tanks and ones on boats.

The absolute worst fuel tanks are on boats down south that get hauled out on lifts for months at a whack and the fuel gets to 80 90 or higher in the tanks with engines that don't get run periodically to circulate the fuel to clean it up.
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