Outboard gas tank setup - SailNet Community
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post #1 of 14 Old 08-23-2013 Thread Starter
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Outboard gas tank setup

On outboard gas tanks not the integrated ones the ones that are connected via a hose their is a twist valve to allow air pressure in so they don't pressure lock.

Obviously this valve has to be open when the engine is running.
If the tank is going to be outside however for several days it is probably a good idea to close the valve so moisture doesn't get in.

I have noticed however that with big temperature changes their can be a lot of pressure or vacuum built up in the tank.

What is the best way to deal with this situation?

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post #2 of 14 Old 08-23-2013
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Re: Outboard gas tank setup

Right or wrong I usually crack the relief valve open... Always gets me too, because I go to prime the bulb, and it won't prime... stupid me has to close the valve to make it prime.

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post #3 of 14 Old 08-24-2013
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Re: Outboard gas tank setup

On the J24 i always kept the fuel tank the lazaret when NOT in use as it is then sitting more or less underwater and the tank stays at a very stable temperature and avoids the whole problem

As much as this seems to upset people the whole vented fuel tank locker is a fairly new innovation on small boats

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post #4 of 14 Old 08-24-2013
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Re: Outboard gas tank setup

As mentioned in an earlier post, I modified my one way vent so it would vent both ways, but found the primer bulb didn't seem to work well. Long story short is to just loosen the filler cap a bit to equalize the tank from excess pressure or vacuum.

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post #5 of 14 Old 08-24-2013
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Re: Outboard gas tank setup

The new tanks have a relief valve set at 5 to 7 PSI, and are tested to withstand that pressure. So no action is required, except to try and keep it out of the sun.

It's a really, really bad idea to keep a gas tank in a lazarette that accesses the bilge. If it is sealed from the bilge, and vents to the cockpit, that's OK.

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Re: Outboard gas tank setup

My solution was to leave the vent open but put a plastic cup over the cap with the vent. It fits tight enough to keep out even driving rain but not so tight as to cause a vapor lock.

Anything wrong with this idea?

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post #7 of 14 Old 08-24-2013
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Re: Outboard gas tank setup

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Originally Posted by MarkSF View Post
The new tanks have a relief valve set at 5 to 7 PSI, and are tested to withstand that pressure. So no action is required, except to try and keep it out of the sun.

It's a really, really bad idea to keep a gas tank in a lazarette that accesses the bilge. If it is sealed from the bilge, and vents to the cockpit, that's OK.
That's the way to go, and so have I.
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post #8 of 14 Old 08-25-2013
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Re: Outboard gas tank setup

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My solution was to leave the vent open but put a plastic cup over the cap with the vent. It fits tight enough to keep out even driving rain but not so tight as to cause a vapor lock.

Anything wrong with this idea?
Well the only thing wrong is that you're venting gasoline fumes. The recent EPA changes to tank designs were intented to address the fact that now a good percentage (10% or so) of hydrocarbons in the air are from evaporation from small gas tanks.

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post #9 of 14 Old 08-25-2013
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Re: Outboard gas tank setup

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Well the only thing wrong is that you're venting gasoline fumes. The recent EPA changes to tank designs were intented to address the fact that now a good percentage (10% or so) of hydrocarbons in the air are from evaporation from small gas tanks.
Good intentions, however before discovering my tank only vented in every time I disconnected the hose from the motor or tank, I was sprayed with gas. So much for preventing vapor escape.

Same thing with California approved gas "cans" with their ultra stupid vent caps which caused me to spill more gas on the ground and me than ever before. I went to a "utility" jug, can't call them a gas can anymore:

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post #10 of 14 Old 08-25-2013
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Re: Outboard gas tank setup

Amen to that, I have an enduring memory of trying to top up the Tohatsu 3.5 hanging off the stern of my Wayfarer, in the middle of San Francisco bay, in a decent chop, with one of those newfangled California gas tanks. The ones that have to be operated with 2 hands.

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