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  Preventing condensation in the gas tank.

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Author Topic:   Preventing condensation in the gas tank.
triblet posted 08-17-2001 04:05 PM ET (US)   Profile for triblet   Send Email to triblet  
Here's a crazy idea I just had for preventing
condensation in the gas tank.

Condensation happens because barometric
pressure and temperature changes cause the
tank to breathe in and out. When it
breathes in, it draws in moist air, which
then condenses when it gets colder. When
to warms up, it breathes out the now
slightly drier air. The cycle repeats each

What if we put a flexible bag on the tank
vent. It breathes out and inflates the
bag a big. It breathes in and deflates the
bag a big. It's the same air and gas fumes,
so there's no new moisture getting in.
Obviously, the bag would have to be safe
for the gas fumes.

I'll try it the next time I store my Montauk.
Oooops, I forgot, I live in California and
we don't winterize. Oh well, maybe one of
the snowbirds on the list will run with the


kingfish posted 08-17-2001 04:51 PM ET (US)     Profile for kingfish  Send Email to kingfish     

Hey, I represent that remark!!


andygere posted 08-17-2001 05:44 PM ET (US)     Profile for andygere  Send Email to andygere     
To take the idea a step further, why not build the fuel tank like a hydropnuematic tank with bladder inside that seperates the liquid (fuel) from the air in a closed system? When it warms up, the bladder compresses, when it cools, it expands. Added benefit would be no need for a primer bulb anymore. Just add a little air to the bladder once a year and you're good to go. Could be tricky when adding fuel to the tank though.....
triblet posted 08-17-2001 06:02 PM ET (US)     Profile for triblet  Send Email to triblet     
You'll still need the primer bulb. That's
to fill the float bowls back up after
they dry up. Nothing to do with air in the

However, I never quite figured out why my
sports car de jour would fire right up after
sitting all winter when an outboard needs
a primer bulb. This includes a couple of
carbureted models with just a mechanical
fuel pump.


Hank posted 08-17-2001 11:55 PM ET (US)     Profile for Hank  Send Email to Hank     
How about just filling the tank ? Very little air volume will mean little volume change during temperature cycling. Little volume change will result in very little moisture condensation.
Tom W Clark posted 08-18-2001 12:07 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

Filling the tank is the convetional wisdom but I think triblet's post might be an extension of the query found here:


Interesting idea. But the problem I see is that the tank and its filler, fuel outlet and vent all need to be sealed in order to withstand a certain small amount of pressure/vacuum. How do you envision sealing the tank on a Whaler?

triblet posted 08-18-2001 08:17 PM ET (US)     Profile for triblet  Send Email to triblet     
Using my Montauk as an example, there are
sealing caps. The bag would be on a separate
vent (the Pate has two places to attach the
tube, I could just use the second one for the
bag, Fuel outlet is probably not a problem,
the bulb has two check valves. Tank is
already sealed.

But again, we don't have to worry about
winterizing. I boat year round, conditions
permitting (admittedly I can get skunked
four weekends in a row in Jan/Feb, but I
don't know in adavance.

Macman posted 08-18-2001 08:21 PM ET (US)     Profile for Macman  Send Email to Macman engineers want to complicate everything! How about closing the vent and calling it good? Works for me!
Dick posted 08-18-2001 08:37 PM ET (US)     Profile for Dick  Send Email to Dick     
You beat me to it.
Closing the vent is the simple answer. It works on mine too.
Tom W Clark posted 08-18-2001 11:08 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Closing the vent is fine for you Montauk and Sport owners but how about owners of boats with built in fuel tanks?
Dick posted 08-19-2001 10:36 AM ET (US)     Profile for Dick  Send Email to Dick     
Sorry about that, tunnel vision.

It is a real problem with built in tanks and I have never seen a solution. What about an inline shut off valve on the vent hose?

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