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Does gas "boil" in a motorcycle tank?

Discussion in 'The Perfect Line and Other Riding Myths' started by tessalino, Oct 12, 2018 at 8:35 AM.

  1. tessalino

    tessalino Long timer

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    I'm reading about the new Triumph Tiger Explorers and heat is a definite issue. The bike is apparently being manufactured to comply with EU environmental regs and the engines are running lean. Which means hot.

    So, on this thread........
    https://www.tiger-explorer.com/index.php/topic,17249.0.html .......gasoline boiling in the tank seems to be an accepted phenomenon.

    I've only been riding since August 2014. Is this common among motorcycles? It's somewhat disconcerting regardless.
    #1
  2. GoGoGavin41

    GoGoGavin41 Wheelie Ergo Sum

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    I would say it's not uncommon to hear gas bubbling in the tanks of many motorcycles and is usually not cause for great concern. Keep in mind that gasoline has an initial vaporization point of something like 100 F which is pretty easily attainable. Just important to be sure that vent lines and such are all working well.
    #2
  3. shinyribs

    shinyribs doesn't care

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    After a hard couple hours of single track you can hear the gas "boiling" in the tank of my XR400. It's not boiling like water on the stove ( the plastic tank would melt first), but you can hear the vapors escaping through the vent hose.
    #3
  4. shovelstrokeed

    shovelstrokeed Long timer

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    Normally, No.
    It would have to get very hot before that would happen. The higher the altitude, lower the atmospheric pressure, the more likely it is to boil.
    Now, that being said, fuel lines in close proximity to very hot objects, like an exhaust header, might experience some boiling but it would be very rare in a fuel injected bike. Fuel line pressures are on the order of 3 bar or 3 atmospheres which would keep the fuel from boiling. The fuel pump is in the tank and the suction side of the pump could wind up far enough below atmospheric pressure to maybe cause hot fuel to vaporize within the pump, in which case you would have a condition known as vapor lock, in that the pump would be trying to pump vapor rather than liquid fuel and it can't do that.
    Proper and functioning venting of the tank is the normal cure for that. Even though fuel can vaporize at 100 F, it also has a very high latent heat of vaporization which tends to cool the fuel.
    Now we come to our "friend" the charcoal canister. These can easily become blocked and prevent proper venting of the fuel tank which can prevent maintaining a pressure in the tank of 1 bar. This can cause that vapor lock issue. If you are running into issues, I recommend removal of that charcoal canister and proper venting of the tank to atmosphere. The EPA will hate this idea but your bike will love it.
    #4
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  5. Bikedude987

    Bikedude987 Been here awhile

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    It's surprisingly easy to get your gas to boil in the tank.

    And, yes, it's EXACTLY like water boiling on the stove. (if you're exceedingly careful, you can boil water in a ziplock bag - water boils just before the bag melts). Gas has a lower vapor pressure than water and boils at a lower temperature, especially if you're up in altitude. Gas begins to boil at only 95*F!

    I would suggest tuning the bike (any bike) that exhibits this phenomenon to run richer, add a fan, and/or line the underside of the tank with heat tape.
    #5
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  6. phughes

    phughes Been here awhile

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    Actually, it depends on the blend. The boiling point is a big range, a little over 100F to almost 400F, depending on the blend. I sincerely doubt much of the gasoline available today boils at 95F, or we would have it boiling daily in any car or motorcycle sitting outside in the Summer.
    #6
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  7. tessalino

    tessalino Long timer

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    I typically fill my tank with pure gas at the end of a ride and park it in my garage. On hot summer nights, the above posts could explain the occasional odor of gas in the garage?
    #7
  8. Grinnin

    Grinnin Forever N00b

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    Just the expansion of the air and fuel inside the tank could push fuel fumes out of the tank vent. So you can get fuel odor way before fuel boils.
    #8
  9. bigdog99

    bigdog99 Weaned and neutered

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    I think most of the fuel heating on modern motorcycles is from the fuel injection return lines. 93 octane has a boiling point of about 122°F at 14psi (1 atm) according to tables. It also has a heat of vaporization of 900Btu/gal so would cool as it vaporized without further external heating, so upper temp should be limited by that.
    #9
  10. Boatman

    Boatman Membership has it's privileges ;-)

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    Boiling fuel in motorcycles is a real thing. Happens to both carbed and injected machines. I've had it happen a number of times, mostly riding in the hot southwest deserts.
    #10
  11. KZJohn

    KZJohn Been here awhile

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    It's not uncommon to see bikes prepped for Baja with the bottom of the fuel tanks covered by heat shielding and the fuel lines inside a shielded covering. There are companies that make model specific heat shielding for dirt bikes. Boiling fuel isn't as big a problem as vapor locking is.
    #11
  12. Vince

    Vince Been here awhile

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    It happened on an Xt500 I owned, but the bike was on fire at the time.
    #12
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  13. texag10

    texag10 Been here awhile

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    I learned of this phenomenon riding a Tuono in stop and go traffic during summer. The thing gets HOT.
    #13
  14. SRG

    SRG SRG

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    Husaberg 70* motors/bikes are famous for this. The exhaust passes close to the tank. When the air temp is hot and the bike is going slowly, the fuel can boil. Known ways of addressing are - run richer fuel (off road/race) map, undertank insulation, ceramic coat on header/exhaust, exhaust pipe wraps, freer flowing muffler, lower temp thermostat, using Engine Ice or sim coolant and optimizing or adding radiator fans.
    #14
  15. glenn2926

    glenn2926 Been here awhile

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    I doubt it. I think it must be liquid to boil. Gas is the result of the boil stage.
    #15
  16. SRG

    SRG SRG

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    ^^Yes, and mind your fag going over the sleeping policeman just before the robot^^
    #16
  17. Strong Bad

    Strong Bad Former World's Foremost Authority

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    Unless sublimation was involved then it goes straight from a solid to a gas.
    #17
  18. foxtrapper

    foxtrapper Long timer

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    Boiling gasoline was the cause of vapor lock, a summer time problem for cars, years ago.

    I’ve had the odd bike that could boil the gasoline in the fuel tank quite well. Usually in the summer, especially when sitting with a very hot engine.
    #18
  19. Bikedude987

    Bikedude987 Been here awhile

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    Which is why I said begins to boil. Pulled directly off wikipedia (not the best source but hey...)
    #19
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