[C320-list] Fuel tank not full

[Troy Dunn]

David-

Not sure why no one has responded.  As I'm sure you know the conventional
wisdom is that leaving the tank partially filled with a hygroscopic fluid
like Diesel fuel in the tank leaving room for condensation you may end up
with water in your fuel, only IF there is in fact condensation, and then
the condensation is subsequently drawn into the Diesel.  Mainesail did a
fairly extensive experiment with an empty tank (
http://www.pbase.com/mainecruising/fuel_tankt_condensation ) but others
would point out that without a hygroscopic fluid in the tank, perhaps...the
accumulated moisture was just evaporating once the humidity dropped again.
  I have not seen a more controlled and well documented experiment, than
Mainesail's.

My opinion is that as long  as your deck plate isn't leaking water into the
tank, and you put some sort of fuel conditioner in your tank for the winter
along with a biocide...you should be fine.    You could always run an
experiment and let us know your results.   Draw off a pint of fuel every
month from your Racor filter and see if you get any water in the fuel.
The water in your fuel tank will sink to the bottom, so it should be the
first thing that is drawn into the Racor each time you do the experiment.
You could also check the Racor before draining to see if any water has
settled there but I think you need to keep drawing off the fuel to get to
what's in the bottom of the tank.

At the end of your winter, my prediction is that you will find no water in
the fuel.   It's a total guess, but I'm thinking that generally in most
areas, winters are dry not humid and without high humidity in the air and
without the fuel in the tank warming sufficiently for the tank to
breathe...condensation will be minimal.   Keep in mind that a 20'x20'x10'
room (4,000 cubic feet) at 100% humidity has roughly 1/2 gallon of water
content.   You'd need a LOT of air exchange and high humidity to get to
that much water.

On the flip side...if you can't sleep at night, by a diesel fuel can, fill
it at your local gas station and top of your tank.

Fair Winds-

Troy Dunn
S/V Wonky Dog
Hull#514

On Fri, Nov 17, 2017 at 3:34 PM, David Nolte <dcnolte at mac.com> wrote:

> I always top off my fuel tank heading into the winter. So when we went to
> do our final pump out our marina had run out of diesel fuel. My 20 gallon
> tank is 3/4 full. Should I worry about condensation and getting water in
> the tank? Has anyone had negative consequences in a similar situation?
>
> Thanks!
>
> David Nolte
> Beach House 0004