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Old 08-24-2013, 12:13 PM   #1
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City: cape charles
Country: usa
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Fresh Water tank air

Hi all, I have 2 FW tanks one main tank at about 190 gal. and another at 30 gal. When I unscrew the cap on the main tank to fill, I notice some vacume on the cap. I checked the vents and all seem clear. Any thoughts on where to start. My boat only runs off the tanks-no city water hook-up. Pump seems to be working fine with either tank. Any thoughts would be appreciated. Thanks

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Old 08-25-2013, 05:36 AM   #2
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Join Date: Oct 2007
Posts: 14,908
Many tank systems vent overboard. This is to allow the owner to fill the tank with no bubbling in the fill pipe.

If it is vented internally the only hassle is some FW might get into the bilge if the owner is really careless on fills. N big deal.

Perhaps a new vent line , just brought up well above the tank top would work for you.

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Old 08-25-2013, 07:49 AM   #3
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The vent line on the middle fuel tank is blocked so drilled a small hole in at the top of the top sight tube. I fill the water about 3/4 and fuel about 1/2. You could just leave the cap loose to allow air as its a water tank. I fill the water tank every week so they are not tight some times forget to put them on.
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Old 08-25-2013, 09:21 AM   #4
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Originally Posted by gar View Post
........I checked the vents and all seem clear....
Gar, If each tanks has a vent and you get vacuum from one when the cap is removed, then one or both of the vents must be blocked. I'm guessing you disconnected each vent hose from the hull fitting and blew through it. Did you check that the hull fittings themselves were clear? My fuel vents were plugged with a hard sandy material deposited (so I am told) by industrious wasps!
If all else fails, read the instructions
If it ain't broke, don't fix it
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