Gas cap vent open or closed when trailering?

[Expidia]

I used to screw the vent cap closed on my portable 6.5 gal tank when I was done with boating for the day.

Especially while trailering home I always closed it.

It's not a built in tank, just a portable 6.5 gal that never leaves the enclosure that Lund builds into their boats. I use it with an outboard.

But many times I of course in my haste to remembering everything I had to do as the boat is moving away from the dock, a short time later I'd stall out because I'd sometimes forget to open the vent

So my Brother in Law a long time boater whose opinion I respect (at least on boating issues) so he says it's not necessary to ever close the vent.

He suggests that the gas sloshes around in the tank while the boats under way and does spill out, so it's not really necessary to close the vent when trailering home either.

So I've been doing it this way for most of last season with no problems and one less thing to have to remember to do anymore when launching and retrieving.

But tonight when I was measuring out the tanks space to see if I can fit a 9 gal in the space the 6.5 is in now . . . when I went to measure it there is of course, a strong smell of gas when I picked up the hatch even though the enclosed space it's in has many vents in the front. The boat is under a boat cover.

So what's the verdict? How many of you just leave that little vent cap open all the time?

 

[CATransplant]

Re: Gas cap vent open or closed when trailering?

I close the vent while trailering, then open it when I park the boat between trips. Then I close it before going to the lake, and open it as part of my setup before launch.

I don't want gasoline sloshing around in the boat while I'm on the road. Seems dangerous to me.

The other option is to buy a real OMC metal tank, which has a vent that operates automatically. Those are sweet. I have one, but it has some rust in it and I haven't gotten around to cleaning it.

 

[amynbill]

Re: Gas cap vent open or closed when trailering?

The other option is to buy a real OMC metal tank, which has a vent that operates automatically. Those are sweet. I have one, but it has some rust in it and I haven't gotten around to cleaning it.

I'll ditto that. When I had my landscaping company, I always picked the self venting tanks. Especially with the cutting crew going from job to job with the tanks bouncing around on the trailer. They work great.

 

[Expidia]

Re: Gas cap vent open or closed when trailering?

I close the vent while trailering, then open it when I park the boat between trips. Then I close it before going to the lake, and open it as part of my setup before launch.

I don't want gasoline sloshing around in the boat while I'm on the road. Seems dangerous to me.

The other option is to buy a real OMC metal tank, which has a vent that operates automatically. Those are sweet. I have one, but it has some rust in it and I haven't gotten around to cleaning it.

On my plastic tank gas sloshes, but it never comes out the vent. If it did it would be spilling out while underway when full. That tank does sound interesting though.

 

[darrklim2]

Re: Gas cap vent open or closed when trailering?

I agree that gas shouldn't slosh out of the vent, but I still close mine while trailering and while sitting. Gas DOES evaporate and at the price gas is now any little bit I can keep from evaporating will save me money. JMHO

 

[Captain Caveman]

Re: Gas cap vent open or closed when trailering?

If you've ever completely filled one of those portable plastic 6.6 gallon tanks, you'll see that gas does start to "bubble" out of the vent sometimes when moving a lot. I have a replacement section of carpet in my boat to prove it!

When trailering I close the vent most of the way, but leave it open just enough that I can hear the hiss of air escaping when I press down on the plastic belly of the gas tank. Several times I have found my plastic tank bulging from heat. The fuel vapors can build up in those things, especially if you leave them in direct sunlight or under a boat cover for several hours. Leaving the vent open slightly keeps the liquid fuel from escaping but allows the vapors to sneak through if under pressure.

This works for me.

 

[drewmitch44]

Re: Gas cap vent open or closed when trailering?

Yea gas is not supposed to slosh out of the vent unless its overfilled. I too normally use plastic portables. I have 4 6 gallons that i swap around as needed to power a 115hp motor. When in season and fishing the boat 3 times a week i never close the vents. When i had the oil injection disabled on the motor though and i was pre-mixing the gas i noticed that the gas would evaporate and leave the oil in the tank and making the mix more oil than i had mixed it. I have never had a problem with gas spilling out of the vent though. And the ammount of gas that evaporates is so small that you will never notice it at all! i would leave the vents open when you are using your boat weekly. If you have any problems then close them.

 

[getinmerry]

Re: Gas cap vent open or closed when trailering?

There's also the moisture factor that everyone seems to be forgetting. The longer the vent is left open, the more possibility of moisture and condensation forming in the tank. I always close mine when not in use. Yes, the pressure can build up if the tank is not stored full, but I would tend to believe that they have been designed to handle that amount of stress.

Chuck

 

[CATransplant]

Re: Gas cap vent open or closed when trailering?

Since I store my aluminum boat outside, I always remove the tank and store it in the tool shed. No sense tempting thieves, and even 3 gal. of oily gas is worth stealing these days, it seems. Besides, I don't like leaving plastic fuel tanks in full sun. They bleach out pretty quick, and the UV can't be good for the plastic.

 

[a70eliminator]

Re: Gas cap vent open or closed when trailering?

I always keep the vent screw closed while not in use, although I did find out one day that when the vent is closed the pressure build up when trailering down the highway was enough to lift the needle seat in the carb and it flooded my engine gas was dripping from carb overflow,(may have had something to do with motor being tipped back while trailering to the lake) I now never leave the hose plugged into the motor when vent is closed.

 

[Expidia]

Re: Gas cap vent open or closed when trailering?

I always keep the vent screw closed while not in use, although I did find out one day that when the vent is closed the pressure build up when trailering down the highway was enough to lift the needle seat in the carb and it flooded my engine gas was dripping from carb overflow,(may have had something to do with motor being tipped back while trailering to the lake) I now never leave the hose plugged into the motor when vent is closed.

Ya that's another reason I've been leaving it open. My outboards an EFI so I have not run into the flooding issue. But when I've kept it closed I have arrived at the launch area, opened the hatch and it sometimes looked like the plastic tank was going to burst at the seams when I leave it closed. That'll run your day when one finally bursts.

I don't really put a lot of faith in how well the seams will hold in a $20 plastic tank. Sad when the 6.5 gal of gas inside cost more than the tank now

I might look into having one custom made up for me or build in a below deck type which probably already has some type of venting system. I can then install a fill spout like the below deck models have. This way I could get at least a 9-11 gal tank in the same space my 6 gal fits into. Maybe even 10 or 11 gal if it's custom made. Then I could put on a self venting cap.

At what the marina's gas prices are going to be this season the upgrade would pay for itself not having to top off while on the lake for a full day's outing. I still always carry onboard an emergency 2.5 gal tank.

My space is roughly 11 high, 14 1/2 deep (or front to back) and 22 1/2 wide. Any one have any ideas on what I could fit in that size hatch space. I lose a gal or two in size with the ready made portable ones in the 8-9 gal size just due to the heights of their caps on a portable.

Even though I could use the 6.5 in there now to transport an extra tank of gas I won't ride in my car with a possible fire bomb, it's simply an unsafe move. It's safer to pay the extra at the marina than bringing it down to the launch area and pouring it in the boat's tank IMO.

I always wondered when I see those pig rolling tanks in the flyers if marina owners who also sells gas get pissed when they see one of their seasonal slip renters trying to roll down their docks with one of those 30 gal tanks with the gas nozzle on them to refill their boats with gas that they bought at some a gas station. All I picture is 30 gallons going up in an accident with this plastic tank on the back of the truck on the way to your boat. I can't believe these thing are legal.

I would think some marina owners would say you can't roll those tanks down their docks because of the inherent dangers when filling your boat around all the other docked boats. I'm sure you can't move your boat to their gas dock and fill it from "your own" tank.

 

[Sliver]

Re: Gas cap vent open or closed when trailering?

This may be a stupid question but am I doing something wrong? I always run my 1981 70HP Johnson with the cap closed assuming it needed to be closed to develope the pressure needed. Is this correct? thanks

 

[Expidia]

Re: Gas cap vent open or closed when trailering?

This may be a stupid question but am I doing something wrong? I always run my 1981 70HP Johnson with the cap closed assuming it needed to be closed to develope the pressure needed. Is this correct? thanks

Incorrect. That vent when open allows the flow of gas from the tank thru the hose.

I'm surprised you have not stalled out yet. Might be a self venting cap or there could be another vent on your tank or your vent cap that screws down to close it no longer seals it closed anymore.

 

[Jack Daniels]

Re: Gas cap vent open or closed when trailering?

I leave mine open all the time even while trailering, i run two steel 6 gallon tanks. I do get the smell sometimes when in storage but its in a garage so i just open the bilge area for venting reasons. I think i get more odor from the outboard than i do the gas tanks. I have never had any trouble with the gas volitalizing away or even fuel leaking from the vent hole. Just my thoughts on teh subject.

 

[Sliver]

Re: Gas cap vent open or closed when trailering?

I would assume then that I have self-venting caps as I have had no problems fuel related. How would I tell? The motor runs great. They are origional OMC label 6 gallon tanks.

 

[jeffnick]

Re: Gas cap vent open or closed when trailering?

Nobody is worried about the fumes igniting while the vent is left open?

 

[DRIFTER_016]

Re: Gas cap vent open or closed when trailering?

I always keep the vent screw closed while not in use, although I did find out one day that when the vent is closed the pressure build up when trailering down the highway was enough to lift the needle seat in the carb and it flooded my engine gas was dripping from carb overflow,(may have had something to do with motor being tipped back while trailering to the lake) I now never leave the hose plugged into the motor when vent is closed.

When the motor is tilted the floats in the carbs open up and allow the pressure in the line to pour the fuel in the line into the carbs until they over flow. I found this out the first week I owned my 90 Merc. It makes quite a mess inside the cowling with oil and gas spilled everywhere. When trailering I always unplug the fuel line. Problem solved.

 

[DRIFTER_016]

Re: Gas cap vent open or closed when trailering?

Ya that's another reason I've been leaving it open. My outboards an EFI so I have not run into the flooding issue. But when I've kept it closed I have arrived at the launch area, opened the hatch and it sometimes looked like the plastic tank was going to burst at the seams when I leave it closed. That'll run your day when one finally bursts.

I don't really put a lot of faith in how well the seams will hold in a $20 plastic tank. Sad when the 6.5 gal of gas inside cost more than the tank now

I might look into having one custom made up for me or build in a below deck type which probably already has some type of venting system. I can then install a fill spout like the below deck models have. This way I could get at least a 9-11 gal tank in the same space my 6 gal fits into. Maybe even 10 or 11 gal if it's custom made. Then I could put on a self venting cap.

At what the marina's gas prices are going to be this season the upgrade would pay for itself not having to top off while on the lake for a full day's outing. I still always carry onboard an emergency 2.5 gal tank.

My space is roughly 11 high, 14 1/2 deep (or front to back) and 22 1/2 wide. Any one have any ideas on what I could fit in that size hatch space. I lose a gal or two in size with the ready made portable ones in the 8-9 gal size just due to the heights of their caps on a portable.

Even though I could use the 6.5 in there now to transport an extra tank of gas I won't ride in my car with a possible fire bomb, it's simply an unsafe move. It's safer to pay the extra at the marina than bringing it down to the launch area and pouring it in the boat's tank IMO.

I always wondered when I see those pig rolling tanks in the flyers if marina owners who also sells gas get pissed when they see one of their seasonal slip renters trying to roll down their docks with one of those 30 gal tanks with the gas nozzle on them to refill their boats with gas that they bought at some a gas station. All I picture is 30 gallons going up in an accident with this plastic tank on the back of the truck on the way to your boat. I can't believe these thing are legal.

I would think some marina owners would say you can't roll those tanks down their docks because of the inherent dangers when filling your boat around all the other docked boats. I'm sure you can't move your boat to their gas dock and fill it from "your own" tank.

Check out West Marine, they have a 12 gal tank that you may be able to get in there. It's 11.75X14X20, I don't know if you can get that extra 3/4" height in there or not.

 

[Expidia]

Re: Gas cap vent open or closed when trailering?

Check out West Marine, they have a 12 gal tank that you may be able to get in there. It's 11.75X14X20, I don't know if you can get that extra 3/4" height in there or not.

I measured tight so I know I have a little more space in all directions. I'll check West out. I was just there an hour ago to returning some extra SS bolts.

Thx