Fuel losses due to leaving vent open

[mastreb]

I routinely forget to close the gas tank air valves on my tanks. They've been open for most of the 18 months that I've had the boat.

So I've finally made it through my first tank of gas (24 gallons). Because I was measuring fuel flow with the engine EMM cable the entire time and reporting it to my GPS head, which kept track of my remaining tank based on summed fuel flow (and presuming that the calibration is somewhere close) I now know how much fuel you can expect to lose to evaporation in an 18 month period: 3 Gallons. Figure 2 gallons per year. This is in sunny (but not hot) southern California.

Remember to close your tank vents when you're not using the boat. 3 gallons is six hours of motoring, and enough to get me from catalina to Dana point.

[NiceAft]

Another aspect for closing the vent on a tank could be the ethanol in the gasoline. Moisture in the air will be separated in the fuel, and you end up with water in the tank.

Don't be so quick to close those vents though. If you do close those vents, and you are in a hot locale such as the east coast of the U.S. in the summer, a closed vent on a rather full tank, on a boat that just sits at its dock/mooring/trailer could allow a plastic gas tank to inflate like a balloon. Something has to give, and with our tanks you hope it's going to be the gasket between the tank and the screw off top.

Let your individual situation be the determining factor.

Ray

[fouz]

I did leave mine open but I had the water in the gas problem like NiceAft is describing. Now I close them and take them out of the boat and put them in my shop.

Southern Alabama so yup, it's hot and humid.

I want to get two 12 gal tanks but I think I'll be better off getting four 6 gal tanks to help with this problem and easy to fill and carry. Just have to find the best ones to get.

[Russ]

Don't be so quick to close those vents though. If you do close those vents, and you are in a hot locale such as the east coast of the U.S. in the summer, a closed vent on a rather full tank, on a boat that just sits at its dock/mooring/trailer could allow a plastic gas tank to inflate like a balloon.

Yes. I had this happen. Tank expanded and looked like it was going to pop. Scary if it did and leaked down to the cockpit drain. Another Mac owner had that happen and it melted the drain hose flooding his cabin with gasoline.

We live in the desert, so moisture is not a problem. However, we once filled a tank very full and when healing heavy found some gas leaking from the vents.

[seahouse]

Interesting info, Mastreb. Now I have an idea of how much fuel I've saved over the years. Closing the vent also excludes air exchange and prolongs the storage life of the fuel.

Whoo boy. This is a sore point with me, and is one of the things that pushes my buttons and drives me absolutely krazy. It has been touched on before, but it might serve as a caveat to others considering these plastic 12-gallon tanks. Here it comes…rant switch “ON”.

I’ve been a lifelong closer of the tank vents to eliminate evaporative emissions, but with this “new” technology with plastic tanks, that’s not, as it turns out from another viewpoint, such a very environmentally friendly procedure as I, and others on the forum who have also reported leaks, have found out.

I got two new 12 gallon tanks (Scepter name- brand, this is a name I now know to be avoided, fouz) with the boat. Between the two tanks, when new (but after I got it home from the dealer and fueled up), I had three separate leaks, at various points in the fittings mounted on the tanks. Sure, my sample size is small, but I would tend to believe that this frequency of occurrence of defects is way too high for this, or any, product.

One leaked into the cockpit, into the transom well, then into the water!!!!! I fixed two of the leak points, but the third is within what appears to be a swaged brass barb fitting at the connector, which doesn’t appear to have an accessible “O”-ring to replace.

It doesn’t matter what the level of fuel in the tank is, (I don’t normally put more than 10 gallons in) as long as the downtube is below the fuel level in the tank, expansion pushes fuel up and out past the connectors on the tanks. I can prevent this by leaving the fuel line attached to the tank, (I used to remove it every time) but that still leaves the other tank, not in use, to leak. The only solution is to leave the vent open all the time. It’s also something that I’ve seen happen to “other” boaters, and not to me, until now.

This is something I consider to be an extremely serious matter (fire/explosion hazard in a marina, toxic to wildlife, a known carcinogen in the environment), but, apparently not serious enough in the minds of the manufacturer of these tanks. Not to mention that one spill (really, even a drop)undoes all the environmental gains made by the latest advances in engine technology.

It becomes a real hazard when removing the tank for refueling, because it always results in some spillage if the tank is not kept perfectly level (just happened this week into the trunk of the car). I plan on making a plug from a piece of urethane with a 1/4” hole in it to fit over the connector for refueling, but haven’t done that yet. At some point I will have to take it apart, assess the problem and replace it, but it’s not too convenient at a time of the year when I’d prefer to be sailing it, not fixing it. Sheesh.

Rant switch “OFF”.

I envy and commend all you guys that close your vents when the engine isn’t running. The tanks should be designed to withstand well over the vapour pressures that are normally encountered during hot days, at least that’s what I think is supposed to be the case. Isn’t the government supposed to step in and say so?

[restless]

If you have an older X, you may want to seriously check the seal between the cockpit side to the fuel tank locker. A proper PITA regarding water ingress, as the above posts show it is also a channel to have your cabin reeking of petrol. Admirals can get particularly agitated by this form of aromatherapy. It causes them to talk incessantly about blowing up, getting headaches, causing cancer etc etc...

[DaveB]

I always have my air vents open a little as temps will expand the tank . I live in SW fL. were temps go above 92 degrees, if tanks are not covered from direct sunlight one can blow the valve or rupture the tank. I always unsrew the vent on both tanks just enough to allow expansion.
Up North with cold nights and warm days will do the same.
Never have fuel in tanks more than 3 mo. with ethonol gas and up to 6 mo. with a Fuel stabilizer.
Ya I know about Up to one year stabilizers, wait that long and you will be doing a carb. rebuild or if lucky doing sea foam wash out.
18 mo. sitting in the carbs is sure to foul everything and have a gum varnish.
Dave

I routinely forget to close the gas tank air valves on my tanks. They've been open for most of the 18 months that I've had the boat.

So I've finally made it through my first tank of gas (24 gallons). Because I was measuring fuel flow with the engine EMM cable the entire time and reporting it to my GPS head, which kept track of my remaining tank based on summed fuel flow (and presuming that the calibration is somewhere close) I now know how much fuel you can expect to lose to evaporation in an 18 month period: 3 Gallons. Figure 2 gallons per year. This is in sunny (but not hot) southern California.

Remember to close your tank vents when you're not using the boat. 3 gallons is six hours of motoring, and enough to get me from catalina to Dana point.

[dlandersson]

The valve is there for a reason - like putting a block of wood in your propeller before you work on it. If you are in a hot location a closed vent on a fairly full tank could allow a plastic gas tank to inflate like a balloon.

I will gladly eat the lost fuel.

I routinely forget to close the gas tank air valves on my tanks. They've been open for most of the 18 months that I've had the boat.

So I've finally made it through my first tank of gas (24 gallons). Because I was measuring fuel flow with the engine EMM cable the entire time and reporting it to my GPS head, which kept track of my remaining tank based on summed fuel flow (and presuming that the calibration is somewhere close) I now know how much fuel you can expect to lose to evaporation in an 18 month period: 3 Gallons. Figure 2 gallons per year. This is in sunny (but not hot) southern California.

Remember to close your tank vents when you're not using the boat. 3 gallons is six hours of motoring, and enough to get me from catalina to Dana point.

[seahouse]

a closed vent on a fairly full tank could allow a plastic gas tank to inflate like a balloon.

Hmmm… And I noticed when I closed the vents passengers were sitting higher in the cockpit seats, but I thought it was because they were so proud to be in a MacGregor.

[mastreb]

18 mo. sitting in the carbs is sure to foul everything and have a gum varnish.

Not to worry: No carbs

And the boat hasn't gone more than six weeks without running in this 18mo. Period. This is So Cal.

Honestly the motor runs as well today on 18mo. old ethanol gas as it did on day 1. The guys at BRP are geniuses.

[raycarlson]

I agree with daveb, 18mo old fuel is a bad maintenance practice,and your begging for problems,ethanol never hurt an outboard,only bad maintenance has.even with stabil i would remove tanks and rinse clean dumping old fuel in car.only time i close a vent is when removing tanks from boat.

[mastreb]

Oh heavens no! My car cost a heck of a lot more than my outboard!

Yeah, I won't be doing this again. I just had no idea how long the fuel would last, this being my first real outboard. From now on I'll just put in a few gallons at a time Unless I'm making a major trip.

[jbousquin]

Just to expand on Seahouse's rant:

I've got two 6 gallon Scepter tanks with "self-purging" vents. These little works of genius were apparently required by the EPA on the tanks I bought. Because they're self-purging, they don't have a vent you can open and close. They're designed to vent to the outside when a certain PSI is reached inside the tank by expanding vapors. I believe it's 5 lbs or something.

Anyway, the bottom line is, they don't work.

Basically, if I leave my gas tanks with the caps screwed on tight, they blow up like a balloon and don't allow the fumes to excape... UNTIL those expanded fumes put so much pressure on the self-venting caps that they blow the little gasket inside the tank and they start to fail. That means the expanding fumes can now get out all the time.... along with liquid fuel as well, especially when heeling.

My dealer just sent me a new cap to replace an old one where the valve was blown, and I'm going to have to get another one for my second tank, too, as it's started leaking as well. This is especially noticeable when the Mac heels, and you see a shiny sheen of gasoline coming down the front of the tank, and onto the cockpit floor where you're usually standing if you're sailing the boat.

My dealer told me to avoid blowing the caps in the future, I needed to unscrew the cap a quarter turn when leaving the boat to allow the tanks to vent... which, of course, defeats the whole purpose of these self-purging vents required by the EPA to "protect" our environment. I just don't see how regularly spilling fuel onto the cockpit floor, and eventually, into the water, accomplishes that.

Just incredibly dumb, if you ask me.

Okay, my rant switch now turned to OFF, too.

[Tomfoolery]

Reminds me of the new gasoline jug requirements for 'spill-proof spouts' that don't seem to work very well, and often make more of a mess than the old-school cans, including the metal ones with flexi spouts (I miss them ). I've given up on the plastic ones for home use, and have 5 gallon metal safety cans with big snap-on funnels.

Oh, and I always crack the vents on my 6 gallon marine tanks. Those things inflating in the sun like a balloon can't be good.

[robbarnes1965]

Very interesting discussion. One very important point left out though. Forgetting to open the vent has much more serious consequences when motoring.

I have had a few occasions to try that one out and it never happens in open water. Always coming out of a lock or into a crowded marina. You usually will have enough fuel in the line to start up without a problem and run just long enough to get into trouble. I occasionally close the vent when it looks like I will be sailing with the daggerboard out of the water or the smell of gas sloshing around gets to me but otherwise I feel safer with it open.