6 gal fuel tanks with vents

[aptled]

just revived an old 70hp Johnson(1980). My old metal fuel tanks were pretty bad, inside and out. I bought some 6 gal plastic tanks and they have a vent on them? First time on water boat ran fine then relized shoot I did not open vents. After opening vents boats would not run and bulb on fuel line was soft. My question is do you vent while in use, as the directions say, and if so how much should you vent them?

Thanks,
Adrian

 

[ezmobee]

Re: 6 gal fuel tanks with vents

Yes they should be vented when in use. Fuel bulb should not remain firm when running.

 

[robert graham]

Re: 6 gal fuel tanks with vents

The caps should have a small vent screw in the middle that you can open 1/2 turn, but if not, then just crack open the fill cap about 1/4 turn just enough to vent, allow air into tank to replace used gas. Good Luck!

 

[Sea Rider]

Re: 6 gal fuel tanks with vents

If you can open the vent screw to max position untill it comes to a no further stop, the better, sometimes with the ride the vent tends to close itself specially when vent has small air opening. I'm refferig to cap vents which are very easy to turn open/close without any finger resistance.

Happy Boating

 

[nwcove]

Re: 6 gal fuel tanks with vents

in my opinion, the vent screw should always be open, to allow air in so your fuel pump can work, and allow air out when the tank is setting and building pressure. the only time i close the vent, is when the tank might set out in pouring rain, then i close the vent and loosen the cap.

 

[JimS123]

Re: 6 gal fuel tanks with vents

Close the vent tight, then push on the top of the tank. You should feel resistance. If you don't, then there is a leak somewhere.

Next, crack open the vent 1/8 turn and push down again. Repeat 1/8 turn if necessary. When the tank now compresses a bit and you hear air whistling out the vent, its set right.

Now, leave it alone! If you close the tank when not in use, that cheep plastic will either explode (expand) or implode depending on whether it gets hot or cold.

 

[Fed]

Re: 6 gal fuel tanks with vents

I think they're supposed to be shut all the time except when running the motor.
Over filling can cause expansion & contraction problems.

 

[JimS123]

Re: 6 gal fuel tanks with vents

I think they're supposed to be shut all the time except when running the motor.
Over filling can cause expansion & contraction problems.

Half full or over full - makes no difference. As the temperature changes, so does the volume of the fuel and air insaide the tank. The older style (and more expensive) metal tanks have self venting caps. So, air goes in or out as necessary. The cheep portable plastic tanks are just not rigid enough to support any pressure or vacuum.

I've seen a tank expand, but then return to normal when the cap was opened. My recurring problem was when a vacuum developed because the weather changed in the Fall and the sides of the tank were sucked in. OPening the vent now did nothing. I literally had to wait for a warm day and put the tank in the sun to get it to pop back out.

The cap is meant to let air and not liquid water in when the vent is open. Don't worry about getting water in the fuel. Never leave the cap loose, that's not a safe practice.

The moral of the story is invest in an OMC metal tasnk and trash the plastic ones - that's what i did!

 

[nwcove]

Re: 6 gal fuel tanks with vents

"quote from jim......Don't worry about getting water in the fuel. Never leave the cap loose, that's not a safe practice."
just curious.....since i have been closing the vent and slightly loosening the cap when the tank, would set, unused in the boat,but only when the weather was saying "heavy rainfall", what makes it not safe? and why should water in the fuel not be a worry?

 

[JimS123]

Re: 6 gal fuel tanks with vents

"quote from jim......Don't worry about getting water in the fuel. Never leave the cap loose, that's not a safe practice."
just curious.....since i have been closing the vent and slightly loosening the cap when the tank, would set, unused in the boat,but only when the weather was saying "heavy rainfall", what makes it not safe? and why should water in the fuel not be a worry?

Getting water in your fuel tank is not a good thing to have happen. The vent is designed to let air in so the tank doesn't implode, or the fuel pump starve from not getting gas. It is designed so that if the tank gets wet liquid water will not go thru the vent. It lets air in, but not a lot of gas vapor. Think about it!!! Its a boat and its meant to get splashed at times.

Now if the boat gets submerged and the tank is under water, all bets are off....LOL!

On the other hand, the gas cap is meant to secure the tank, not vent it. What if you forgot to put the cap back on? Likely you might spill gas. Bounce around with a loose cap for awhile!

Just read the directions. The guy that invent the tank knows more about it than me!

 

[Fed]

Re: 6 gal fuel tanks with vents

The plastic tanks I've seen have been designed so that they can't be overfilled or they have a fill line molded into the tank.
The air space is there so the tank can compress or go into vacuum without distorting the tank to the point of failure.
The gas can expand but it won't compress where as the air can compress without expanding.
I wonder if the OP had a bad fuel pump and was running on tank compression until he undid the breather, stranger things have happened. LOL

 

[nwcove]

Re: 6 gal fuel tanks with vents

lol Jim, my fault. guess i should have been more specific about my kinda of boating. small boat, along the shore, in ideal weather. slim chance of of bouncing around....unless its a wake from a bigger boat!
bottom line.......the tank needs venting, one way or another....whether its running or setting idle.

 

[Home Cookin']

Re: 6 gal fuel tanks with vents

I've seen empty tanks with the tops on tight, expand and contract. The only time the cap and vent are tight is when you are transporting the tank, to prevent spillage.
I don't trust the little round vents against hard rain. But look how high the rim is under the cap--an inch? no rain water is going to rise up under there if the cap is loose a little.
Due to problems with ethanol it's best not to leave them out in the weather if you can help it anyway, for any length of time.

The plastic tanks I've seen have been designed so that they can't be overfilled or they have a fill line molded into the tank.
The air space is there so the tank can compress or go into vacuum without distorting the tank to the point of failure.
The gas can expand but it won't compress where as the air can compress without expanding.
I wonder if the OP had a bad fuel pump and was running on tank compression until he undid the breather, stranger things have happened. LOL