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Old 02-17-2011, 11:09 AM
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Default Can gas evaporate out of a tank?

I have a small 6 gallon tank in my boat. It's all I need as I don't make many long runs. Anyway, I just know I filled it up AFTER the last time I used the boat in early january. I'm pretty sure I didn't have the vent closed though. I pulled the boat out last night to run it on the hose because it's been a month, maybe even a little over. I noticed that I had a half of a tank. It seems that one of three things has happened:

1. I am dillusional and didn't actually fill up after I used it last
2. I have a leak in the tank (checked all over and couldn't find one)
3. I lost 3 gallons to evaporation and/or sloshing through the vent hole going down the road

what seems most likely?

oh i almost forgot: my boat is stored outside under a cover
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Old 02-17-2011, 11:19 AM
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Gas can EASILY evaporate (take 16oz of gas, put it in an open containere and leave outside for 3 days of low humidity ..... it will all be gone by the 3rd day).
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Old 02-17-2011, 11:20 AM
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I don't think it would have evaporated up to half a tank. Maybe 1/4, but not half. If you drove it an extended amount of time with the vent open, that COULD have contributed to it. If you drove like 4-5 hrs, open vent, at 65-70, PLUS a month of standard evap, i would say you could be missing 3 gallons.
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Old 02-17-2011, 11:26 AM
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Can gas evaporate out of a tank? Yes.

3 gallons in one month because you left the vent open? Not hardly.

Something else is going on here.
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Old 02-17-2011, 11:41 AM
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Where was the tank in relation to the altitude of the carb?
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Old 02-17-2011, 12:08 PM
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Seems like a lot to lose to the angels but I've never left mine unsealed that long. Does the rest smell bad?
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Old 02-17-2011, 12:34 PM
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Quote:
Where was the tank in relation to the altitude of the carb?
well below and the fuel line was disconnected...... hmmmmmm just had a thought. I might need to check and make sure my fuel line isn't the culprit
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Old 02-17-2011, 03:20 PM
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I had that happen, but then I realized my gauge had gone bad.
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Old 02-17-2011, 03:40 PM
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gas can evaporate. especially if there are teenagers with short peices of garden hose available.
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Old 02-17-2011, 03:52 PM
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Yes
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Old 02-17-2011, 04:06 PM
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I had a couple of 6 gallon plastic tanks with "automatic" vents. The vents would allow air into the tank but not back out. If left in the sun, the gas in the tank would expand and flow into the engine. I could see these pumping the tanks dry with enough heating/cooling cycles.
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Old 02-17-2011, 04:41 PM
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Not doing the math right now but there's no way enough air is moving through that tank to allow that much evaporation. If the tank had the top cut off, it was in direct sunlight in the summer, and you had a fan moving air over the tank. It might evaporate 3 gallons. But I'd still be impressed if it was that fast.

You can do the complicated rate of evaporation calculation if you know the rough airflow in the tank, and temperature. You can estimate pressure and surface area of the fluid. You'll find that 3 gallons is near impossible.
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Old 02-17-2011, 04:53 PM
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Do you have teenage drivers? My 5 gallon can of gas for my lawn tractor "evaporates" all of the time.
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Old 02-17-2011, 11:00 PM
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Not to hijack the thread, but I've been wondering about the rate of evaporation out of a boat's tank and how it relates to economy. Most gas versus diesel arguments ignore the loss of gas through evaporation if using flowscan data. I've been told that in Northern Australia, "petrol" vehicles are almost unheard of because loss can be up to 40% in the hot climate. A gas powered boat in a hot climate, with constant agitation thrown in, could approach that 40% loss. I know I've operated a big gas guzzling boat in a hot climate and the fumes are a visible constant stream out the vents. Any thoughts?
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Old 02-17-2011, 11:14 PM
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I found the culprits that took your gas. They say they are siphoning gas, getting rum, and goin on a cruise, your lucky they didn't take your whole boat on a cruise

http://www.youtube.com/watch?v=RXtePW4v8zs
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Old 02-18-2011, 04:52 AM
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Quote:
Originally Posted by jmarlin View Post
Do you have teenage drivers? My 5 gallon can of gas for my lawn tractor "evaporates" all of the time.
Glad I'm not the only one with a magic gas can.
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Old 02-18-2011, 08:22 AM
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Quote:
Do you have teenage drivers?
hell, i'm only 23 myself. My question...... how did I not think of this when I was 16? I mean, I had infinite wisdom back then so I'm sure I would've been able to explain the magic gas can to my dad.
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Old 02-18-2011, 08:26 AM
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I want a magic gas can that tops itself off!
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