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Brad777's avatar
Brad777
Explorer
Apr 15, 2014

Gasoline Evaporation of 3/4 gallon per week ???????

I have a 1995 Bounder with a 75 gal. gas tank. I am loosing about 3/4 gal. of fuel every week because of what I think is evaporation. I have looked for leaks and find none. I followed the vent tube from the gas tank back to the gas cap area and it looks in tack. The vent tube is a closed loop next to the main gas fill hose. The generator does draw off of the main fuel tank but I don't see any problems with it. I also tried to seal off the gas cap very tight with saran warp to stop the evaporation and that did nothing ? Is it possible that this is normal amount of evaporation ? My climate in So. California is about 75 -85 degrees. Any help on this question would be very much appreciated.

Thanks,
Brad
Class A
  • darsben's avatar
    darsben
    Explorer II
    Apr 15, 2014
    Tom N wrote:
    Have you considered someone syphoning you gas??

    II bit my tongue but gave up.
    SERIOUSLY someone siphoning 3/4 gallon every week!

    On the other hand I have never thought about how much I lose in a week. But the difference could be remotely related to temperature as gas expands and contracts. MY follow up question to the OP is "Is the loss cumulative so 3/4 this plus 3/4 more next week so that after a while you have lost 3 or 6 gallons."
  • naturist's avatar
    naturist
    Nomad
    Apr 15, 2014
    3/4 gallon per week would be a small leak, you know. I make that out to be about 8.4 drops per minute. (assuming a drop size of 30 per ml, common for water, not so sure about gasoline)
  • msmith1199's avatar
    msmith1199
    Explorer II
    Apr 15, 2014
    Just curious, how do you know it's 3/4 of a gallon a week? That seems difficult to measure. I'm not familiar with gas evaporating out of a closed up gas tank like that at all.
  • timmac's avatar
    timmac
    Explorer
    Apr 15, 2014
    dakdave wrote:
    how are you determining 3/4 gal a week?


    That's what I want to know, how does one determine the amount unless you pump it out and measure the amount each week..

    To the OP its normal for some evaporation especially above 80 degrees, maybe the age has a factor with the gasket at top of tank where the pump goes, gasket wore/dryed out, dry rot on certain fuel lines etc will cause more evaporation, difficult to see some of these lines, even more difficult to see top of gas tank, also replace the old fuel cap, those also over time will loose there seal.
  • Brad777's avatar
    Brad777
    Explorer
    Apr 15, 2014
    I do have a locking gas cap and it has not been tampered with.
  • Brad777's avatar
    Brad777
    Explorer
    Apr 15, 2014
    Yes, the loss is cumlative. If I check it in two weeks it is 1.5 gallons and so on.
  • Brad777's avatar
    Brad777
    Explorer
    Apr 15, 2014
    I have determined it is 3/4 of a gallon a week by filling up the gas tank to the brim and then doing the same at a later date measuring how much fuel it will take to the brim again.

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