wrote:


Oh, but they DO. Any variation in temperature of the air surrounding
the tank will cause a pumping action. Temp goes up, the air in the
tank expands and finds a way out to create equilibrium. Temp goes
down, the tank inhales air containing moisture.

So? The moisture just goes right out again with the air. In the case of
the empty tank for the winter Rich was discussing, there is no thermal mass
of fuel to create the temperature differentials that would create
significant condensation. Even in the case of tanks partially full of fuel
condensation on a tank top is unlikely to be a significant issue (see my
reply to Larrry).

--
Roger Long

wrote

But the small amount of water that enters each time the surroundings
cool, stays there and accumulates. Over a 4 or 6 month layup?

Not necessarily. The surroundings have to cool differerentially or to the
extent that there is water on every surface. Even then, the water doesn't
necessarily fall off the surface and into the fuel. I was in my boat nearly
every day working on it last winter and I never saw conditions that made me
think that the tank top would have been covered with water drops. I also
kept my tanks drawn down most of the winter because I was installing my new
fuel system. My boat was in a shed that warmed up a lot with a very damp
floor so there was lots of temperature differential.

When in turmoil, when in doubt, always try a little perspective:

The "pumping action" of temperature changes is orders of magnitude less than
the pumping due to fuel sloshing around with boat motion.
The temperature differentials in summer with cool water and hot sun are much
greater than for a boat hauled out in the winter.
The cold air of winter is generally drier. Condensation happens because air
cools and can't hold as much moisture. Much of that process has already
happend by the time winter air gets into your tank.

If filling your tanks is really vital in winter, big time problems in summer
is what we would be discussing here.

It still a good, but not vital, idea to minimize fuel surface area contact
with air over long periods of storage. One way to do this is to fill the
tanks into the vents. Another is to empty the tanks. I can't do the latter
so I do the former. Not doing anything is unlikely to lead to problems so
severe they can't be dealt with with something like Startron.

My boat was laid up for six years near Detroit by the former owner with a
partially filled fuel tank and I had to deal with it after I bought it. The
fuel turned to partly to jelly that wouldn't go through the filters and
there was a mega clean up but there was no water in the bottom of the tank.
There was no real alge growth either. The fuel just evaporated off ligher
elements, oxidized, and aged.

--
Roger Long

On Thu, 13 Nov 2008 09:02:01 -0500, "Roger Long"
wrote:


When in turmoil, when in doubt, always try a little perspective:

Reminds me of the Honda owners who insist on changing brake fluid
every couple years because brake fluid is hygroscopic.
They love that word.
Doesn't matter that the braking system is closed to the atmosphere.
Change that brake fluid. And use Honda fluid to be "safe."
When I mentioned the 13-year old brake fluid in my Celebrity was
performing just fine I was accused of being a road menace.
That's why I love usenet.

--Vic

On Wed, 12 Nov 2008 16:45:06 -0800 (PST), RichH
wrote:

EMPTY tanks dont magically fill up with water because of a mysterious
'condensation process'. :-)

There is a simple explanation. In a half full tank, the fuel will
overlie the water and keep it from evaporating, when it warms up
during the day.

Casady

On Thu, 13 Nov 2008 06:34:37 -0500, wrote:

EMPTY tanks dont magically fill up with water because of a mysterious
'condensation process'. :-)

Oh, but they DO. Any variation in temperature of the air surrounding
the tank will cause a pumping action. Temp goes up, the air in the
tank expands and finds a way out to create equilibrium. Temp goes
down, the tank inhales air containing moisture.

In dry weather, the tank will breath dry air, and evaporate any water
that is there. Unless the tank is NOT empty and the fuel layer
prevents evaporation of the water. A teaspoon full is all it takes.

Unless of course you think your tank is completely pressure sealed, of
course.

why do the fuel caps on cars hiss at you when you open them, if they
are not sealed?

Casady

http://www.yachtsurvey.com/myth_of_c...fuel_tanks.htm

On Thu, 13 Nov 2008 09:02:01 -0500, "Roger Long"
wrote:

My boat was laid up for six years near Detroit by the former owner with a
partially filled fuel tank and I had to deal with it after I bought it. The
fuel turned to partly to jelly that wouldn't go through the filters and
there was a mega clean up but there was no water in the bottom of the tank.
There was no real alge growth either. The fuel just evaporated off ligher
elements, oxidized, and aged.

Algae is a green plant, does photosynthesis and all that, and cannot
survive without light. Fungus can grow in fuel tanks, the stuff feeds
on the fuel, but it has to have water. They have antifungus, anti
water additives for jet fuel. The first Learjets lacked fuel heaters,
and you added Prist, from an pressurized can, through a hose clipped
to the fuel nozzle. That way it mixed.

If you evaporate all the light fractions, could this decrease the
solubility of the wax? Maybe wax had something to do with the jelly.
Cold fuel waxes out, and it plugs filters. [One solution is to mix
50/50 with #1 fuel. At least one station in Des Moines sells the
blend, during the Winter.]

Casady

On 2008-11-13 10:56:30 -0500, Gordon said:

http://www.yachtsurvey.com/myth_of_c...fuel_tanks.htm

How did you find that? I went there first of course, but couldn't find it.

"Wasted" a bit of time, as usual, as I found a half-dozen articles of interest.

--
Jere Lull
Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

On Wed, 12 Nov 2008 16:45:06 -0800 (PST), RichH
wrote:

Common knowledge is entirely faulty.

Fuel oil when manufactured (cracked, etc.) is rendered essentially
'dry'. Water (vapor in the air) 'equilibrates' eventually until the
oil is saturated with water from the atmosphere ..... and only after
the oil is SATURATED with water does the 'condensation' become
apparent. Simple speak: if your fuel is condensing water it means
that its laid around with an open vent too long and its now LOADED
with water.

How much is "LOADED" in ppm?


The BEST is to totally empty the tank for the winter, take home the
fuel and burn it in your heater.
EMPTY tanks dont magically fill up with water because of a mysterious
'condensation process'. :-)

The threat of water in the fuel is real, but it shouldn't be a problem. You
must have a business process in place to manage the problem. The most likely
cause is being delivered fuel with already absorbed water. The second threat
is fuel is hygroscopic and absorbs moisture from the atmosphere. This is a
low threat in cold temperatures because the air will not contain much water.
However, this is a big problem in warm humid climes. The consequences are
tank corrosion, bacterial growth and fuel system failure. The decision to
fill your tanks are really fuel cost and saving opportunities based. Your
protection against the threat are corrosion proof tanks, biocide additives
and a centrifuge water/fuel separator (fuel polishing system). The risk
cannot be avoided, only mitigated.
Steve

"Marc Auslander" wrote in message
...
Common knowledge is that we should top up our fuel tank for the winter
sleep. Argument is that otherwise the temp changes will continuously
condense water into the tank, as moist air is pulled in, condensed,
and then expelled.

I have no doubt that the effect is real, but wonder how big it
actually is. How much water per gallon (or liter) of air would
condense in one cycle of some plausible temperature range and some
plausible outside dew point?

(I think I know how to calculate this, but wonder if its already been
done?)