Gas cap: Air rushing out upon removal when fueling. Normal? | FerrariChat

Gas cap: Air rushing out upon removal when fueling. Normal?

Discussion in '348/355' started by ready321now, Apr 29, 2014.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. ready321now

    ready321now Formula Junior

    Jan 5, 2013
    484
    New Jersey
    When I stop for gas for my F 355, I remove the cap and a LOT of air rushes out. Is this normal?

    Thanks in advance. -Brian
     
  2. vvassallo

    vvassallo F1 Veteran
    Silver Subscribed

    Aug 4, 2006
    8,281
    Palos Verdes
    Full Name:
    Vince V
    Normal. The less fuel in the tank the more rushing air. Remember, your fuel sustem is pressurized.
     
  3. ready321now

    ready321now Formula Junior

    Jan 5, 2013
    484
    New Jersey
    Thank you. It came as a surprise when a Maylasian typhoon came rushing out every time I fueled. If It's normal, I guess I have nothing to worry about. Never had a pressurized system before!
     
  4. Falcon Wing

    Falcon Wing Formula 3

    Aug 4, 2010
    1,294
    Colorado Springs
    #4 Falcon Wing, Apr 29, 2014
    Last edited: Apr 29, 2014
  5. 166&456

    166&456 Formula 3

    Jul 13, 2010
    1,723
    Amsterdam
    #5 166&456, Apr 29, 2014
    Last edited: Apr 29, 2014
    Not normal, sorry. The fuel system is not pressurised, why would it be and by what?
    No. You have a problem with the anti evaporation system, either in the rollover valve, charcoal canister, or purge valve. Is gas flowing out or into the tank when this happens? And if you let that gas difference clear, close the cap firmly again, go for a short drive, and reopen the cap, does it then happen again? If yes, then the purge valve is stuck open or the canister blocked. There are some more ways and things to test but that is a good place to start. A slight whoosh is ok but it should be really light. The canister can be blocked in multiple ways, with different symptoms.
    Please note that you would not be the first to have a ruptured or imploded tank or surrounding lines from a defective evaporation system.
     
  6. AceMaster

    AceMaster Three Time F1 World Champ

    Feb 6, 2009
    34,548
    Ontario, Canada
    Full Name:
    Mike
    I think you mean if the air was actually getting sucked in, correct?
     
  7. ready321now

    ready321now Formula Junior

    Jan 5, 2013
    484
    New Jersey
    Thanks....to confirm, the air rushes OUT, not in.
     
  8. 166&456

    166&456 Formula 3

    Jul 13, 2010
    1,723
    Amsterdam
    #8 166&456, Apr 29, 2014
    Last edited: Apr 29, 2014
    Diagnosis depends on the conditions at which the pressure difference occurs.
    If it is overpressure on a hot day, it is likely the rollover valve or canister that is blocked. It may also be that lines got blocked because of charcoal out of the canister.
    If it is underpressure, it can be caused by cooling surrounding temperatures or as simple as the fuel leaving the tank creating underpressure if outside air is somehow blocked from entering, again by a blockage somewhere. It may also be that the purge action during driving actually vacuums the tank, possibly imploding it. But that can only happen with a stuck purge valve and/or a blocked canister.

    Sometimes you have both, overpressure on a hot day, and underpressure with an empty tank or after a drive. As said, plenty of tests to do, because there are a few components to be blocked or otherwise defective. The system is not complex but it may be complex to diagnose which part is the problem.
     
  9. ready321now

    ready321now Formula Junior

    Jan 5, 2013
    484
    New Jersey
    What happens specifically is that as I am unscrewing the cap, air begins to rush out, and as soon as I get the cap off, it pushes out the rest of the air quickly, and then it stops almost immediately after the cap is off. So are we at a consensus that this is a problem? Or is this acceptable and expected from a "pressurized" fuel tank?
     
  10. ready321now

    ready321now Formula Junior

    Jan 5, 2013
    484
    New Jersey
    The air rushes out...and nothing happens while I am fueling because the rushing air situation is over as soon as the cap is fully off. Would that help? I am wondering if I can isolate the problem given my symptoms.
     
  11. ready321now

    ready321now Formula Junior

    Jan 5, 2013
    484
    New Jersey
    I just walked over to the car, which has parked for a week (awaiting new manifolds). I unscrewed the cap and I heard absolutely no air this time. I recall the pressure seems to build over longer trips, when the tank is closer to empty.
     
  12. Wade

    Wade Three Time F1 World Champ
    Owner

    Mar 31, 2006
    32,793
    East Central, FL
    Full Name:
    Wade O.
    My 348 does this,over-pressure after driving for awhile. Short trips aren't so bad but once, on a hot day with extended stop and go traffic, the car was making a weird noise after shutting down. Sort of like a muffled fog horn, but very noticeable and coming from the fuel cap area. When I removed the cap a huge amount of air whooshed out for what seems like 10 minutes or so. Also, it sort of sounded like the fuel was boiling, if that's possible. Worth noting, the car drove well, engine smooth and no indication of over-heating at all.

    Finally, with the exception of an F-4 Phantom, I've never felt an engine bay that operated as hot as this car does. My friend's 348 was the same...
     
  13. SoftwareDrone

    SoftwareDrone F1 Veteran
    Sponsor Owner Rossa Subscribed

    Jan 19, 2004
    7,504
    San Jose, California
    Full Name:
    Mike
    A Ferrari Fart??
    :D
     
  14. Wade

    Wade Three Time F1 World Champ
    Owner

    Mar 31, 2006
    32,793
    East Central, FL
    Full Name:
    Wade O.
    #14 Wade, Apr 29, 2014
    Last edited by a moderator: Sep 7, 2017
    Seriously... it was pretty embarrassing. ;)

    Must be the ethanol!

    But really, there aren't many parts to the system. Charcoal canister? I hope not.

    .
    Image Unavailable, Please Login
     
  15. Wade

    Wade Three Time F1 World Champ
    Owner

    Mar 31, 2006
    32,793
    East Central, FL
    Full Name:
    Wade O.
    #15 Wade, Apr 29, 2014
    Last edited by a moderator: Sep 7, 2017
    What's baffling to a 348 newbie like me. Item E (Evaporative Emission Control System) in both the Owner's and Workshop Manual is called the Anti Rollover Valve (see image in the above post).

    However, the same "item" (although marked as 10), in the fuel system diagram, is called the Tank Vent Valve.

    .
    Image Unavailable, Please Login
     
  16. Wade

    Wade Three Time F1 World Champ
    Owner

    Mar 31, 2006
    32,793
    East Central, FL
    Full Name:
    Wade O.
    But this post from 2005 is pretty interesting:

     
  17. amattox1

    amattox1 Rookie

    Nov 30, 2013
    44
    Bay Area CA
    Full Name:
    AMattox
    Been wondering about this myself, as my car does this as well. (definitely air rushing out not in) I did find a thread that discuses bad purge valves being the cause of strong vacuum in the gas tank. Could a bad purge valve also cause pressure to build in the tank as well?
     
  18. Ricambi America

    Ricambi America F1 World Champ
    Sponsor Owner

    Search Fchat for "moo-ing" sound of 348 fuel system.
     
  19. ready321now

    ready321now Formula Junior

    Jan 5, 2013
    484
    New Jersey
    Sounds like we are in the same boat. Though, "vacuum" issues sound more like the cars sucking in the air as opposed to it blowing out like ours, no? I'm still learning about this issue obviously. You pose a good question.
     
  20. whyte

    whyte Formula Junior

    Apr 25, 2006
    404
    Merritt Island, FL
    Full Name:
    John C
    At the risk of repeating some stuff, your fog-horn is the sound of a properly functioning "2 way valve." It has a rubber diaphragm in it that allows excess fuel vapor to vent from the tank, into the charcoal canister.

    The diaphragm has a minimum pressure at which it vents, so I suspect there may be some pressure in the tank due to expansion or contraction of the air / fuel vapor that can be relieved via opening the sealed cap, however it is also important that the valve kicks in when too much pressure is in place. Otherwise, bad things happen to gas tanks.

    I actually cleaned my valve this week. A simple blast of compressed air generated the familiar fog horn as the pressure relieved. And yes, this same valve is also what keeps your fuel from running out if you flip the car, so it is definitely prudent to check it out. It's located next to the charcoal canister up under the fender a bit. Trace the hoses from the charcoal canister back and you'll find it.

    Wade: Bring yours by sometime and I'll be happy to show you where it is / how to check it. :) Heck, I'll even clean it for you, for a six pack.
     
  21. ready321now

    ready321now Formula Junior

    Jan 5, 2013
    484
    New Jersey
    Is this 2 way breather valve one of the parts in the schematic posted above by Wade?
     
  22. whyte

    whyte Formula Junior

    Apr 25, 2006
    404
    Merritt Island, FL
    Full Name:
    John C
    Yes. I'm not sure why it is labeled as it is on the diagram. It is, however, E in the diagram, called a "check valve" there. Later in the same documentation, it is shown in the figure and the text as a "Two Way" valve.

    This part handles pressure mitigation for vacuum and excess pressure in the tank, in addition to being a roll-over safety device.

    Follow the line from the charcoal filter that goes up under the fender. You can't miss it.
     
  23. cuneo

    cuneo Formula 3
    Silver Subscribed

    Nov 20, 2006
    2,428
    My 1995 355B has done the same thing as the OP's car for 8 years and 25k miles. Fill tank, drive a long way, and when the tank is almost empty open the gas cap to fill and air rushes out for anywhere from 1 to 4 seconds. I have to hold onto the cap sometimes so it doesn't pop off and hit the paint! That's always after a fast drive on a 1/4 tank, though.

    Never had air rush in.
     
  24. whyte

    whyte Formula Junior

    Apr 25, 2006
    404
    Merritt Island, FL
    Full Name:
    John C
    The manual indicates the tank can have either positive or negative pressure. Thus the "two way" valve is made to fix both of those.

    If you have substantial pressure when you take the cap off, it is not working properly. Mine stopped working about 8 months ago and I finally fixed it last week. (not sure if this applies to the 355)
     
  25. ready321now

    ready321now Formula Junior

    Jan 5, 2013
    484
    New Jersey
    #25 ready321now, Apr 30, 2014
    Last edited by a moderator: Sep 7, 2017
    Thanks. This is the first thing I am going to check. As a matter of fact, I am going to go find it right now. Let's see.

    Ok I see the plastic canister with two hoses attached. It's behind a metal plate/ guard. I followed the hose, and found this: so I guess the red item should be checked?
    Image Unavailable, Please Login
     

Share This Page