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Subject: TWL: Fuel Stability - was - Worst Boating Adventure
From: Alex Hirsekorn (alexh@XXX.XXX)
Date: Mon Jan 07 2002 - 04:32:56 EST
----- Original Message -----
From: "Joe DellaFera" <samakijoe@XXX.XXX>
>
> (Does anyone out there with many years of "Diesel burning" experience have
> the opinion that diesel today is less stable then it was years ago?)
>
Hi Joe,
Today's diesel is probably less stable than the fuel available prior to the
government's requirement for low sulfur fuel. I personally doubt, however,
that
there's enough difference to matter to most folks.
Prior to the low sulfur requirement diesel tended to be largely aliphatic in
composition meaning that it was [mostly] made of straight chain molecules.
Aliphatics have the advantages of better lubricity and better oxidation
resistance (They have the disadvantages of a higher cloud/pour point and
less energy per pound).
Enter the US Government.
The new rules mandate that 'on-road' fuel have far lower sulfur levels
(0.05% vs. 0.5%). It turns out that the cheapest way to comply with that
rule is to make diesel with a higher percentage of aromatic components.
Aromatics have poorer lubricity and oxidation resistance.
You probably recall that there were complaints about diesel lubricity
immediately after the rule change. The oil companies addressed those
problems by adding lubricity additives at the refinery. OTOH: There weren't
any meaningful complaints about fuel stability for the simple reason that
99.99% of the diesel fuel purchased is used up long before it approaches its
shelf life. For example: At my last job we advised customers to NOT buy more
diesel than they would use in a month or so based entirely on the cost of
the money. It was a better deal for such customers to utilize our cardlock
fueling system than for them to sit on inventory. As a result, most of our
customers were burning fuel that had been refined no more that a couple of
weeks (and often less than one week) prior to use. IOW: Shelf life just
isn't an issue in the marketplace as a whole.
As far as what the shelf life is for fuel in a boat's tanks: Who knows?
There are about a zillion variables that affect any specific situation:
- Temperature - I can't back this with statistics but it only seems logical
that fuel will oxidize faster in Florida than it will here in Washington.
- Dryness - Dry fuel is more stable than wet.
- Cleanliness - Some contaminants can accelerate oxidation so cleaner fuel
will last longer.
- Age and condition - How old was the fuel when you got it and how well had
it been cared for?
There isn't anything you can do about the climate that your boat lives in
but it's helpful to keep that variable in mind if you're comparing notes
with people in other parts of the world.
The other things I mentioned are all interrelated. For best longevity you
want to buy the cleanest and driest fuel possible and then keep it that way.
Buying fuel is like buying coffee, cheese, or fish; You're almost always
better off buying from the busiest dock in your area. The busy ones turn
their inventory the fastest and are more likely to keep an eye out for
things like water contamination. Keeping your fuel clean and dry can be as
involved as you want to make it or it can be as simple as just practicing
good housekeeping. Good housekeeping should be the starting point for any
sort of fuel management anyway; Keep the tanks full whenever possible, keep
the fuel cap(s) secure and snug except when fueling, don't introduce dirt
and water when you open the cap for fueling (or when you put the nozzle in
for that matter); It's not rocket science!
As with so many things about boating, the best thing you can do to avoid
fuel oxidation is to just use the boat a lot so you'll burn the fuel before
it can go bad! If that isn't feasible then adding a fuel stabilizer when you
fill up is cheap insurance and will (at the very least) do wonders for your
own peace of mind.
Freshly yours,
Alex
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