Prius Bladder System-Tip to Restore Tank Capacity

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by hb06, Oct 24, 2006.

  1. hb06

    hb06 Member

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    --Wikipedia

    Prius-Fuel Tank/Gauge

    "The North American Prius uses a rubber bladder system besides a charcoal filter for gas vapor emissions control. However, the rubber is temperature sensitive and will shrink/stiffen in cooler weather lowering the tank capacity from the default 11.9 gallons, and contributing to a wildly inconsistent fuel gauge. This is similar to the "memory" in NiCad batteries.

    "Slow filling of the tank with careful "burping" of the fuel inlet past the first "click-off", without spilling, will stretch the bladder back out and restore the original tank capacity."

    Page 206; The tank is 45L (11.9 gal., 9.9 Imp.gal) and decreases by 5L (1.3 gal., 1.1 Imp.gal) @ -10°C/14°F."
     
  2. Beryl Octet

    Beryl Octet New Member

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  3. Cheap!

    Cheap! New Member

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    If we put our heads together, we should be able to figure out how to install a small hose that sits just behind the gas cap and runs to the top of the bladder. A burp hose so to speak that would let air run from top of the bladder to the top of the fill hose, then on to the gas station recovery vents on the nozzle.

    Is anyone working on this?
     
  4. Charles Suitt

    Charles Suitt Senior Member

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    Quote: " a small hose that sits just behind the gas cap and runs to the top of the bladder "

    One of the super low pollution features *IS* the bladder system to prevent gasoline fumes from escaping into the atomsphere when fueling the Prius. Sounds like such a 'hose' would defeat that feature if actually connected to the bladder itself. Can't see a practical way to connect such a hose to the station's vapor recovery system.

    Perhaps you are thinking of a hose to the top of the 'tank' structure in which the bladder is contained to relieve any back-pressure in the tank. Anyone here know whether there is a back-pressure relief valve or system to allow bladder expansion within the tank?
     
  5. eagle33199

    eagle33199 Platinum Member

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    The only real problem with that is: what happens when the tank is full? with the hose there, it seems to me that the excess would just travel up the hose and into the gas stations recovery system... with no pressure infront of the pump, the auto shutoff wouldnt work, and we would end up giving them tons of extra money... all for a few extra miles of driving between pumps...
     
  6. Cheap!

    Cheap! New Member

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    <div class='quotetop'>QUOTE(Charles Suitt @ Oct 24 2006, 01:19 PM) [snapback]337439[/snapback]</div>
    Sorry this is so crude, I just don't have time to draw this right now.

    [attachmentid=5461]

    <div class='quotetop'>QUOTE(eagle33199 @ Oct 24 2006, 01:21 PM) [snapback]337444[/snapback]</div>
    The hose would be very small since it only needs to let air bleed off into the closed system. It could be in the main fill line below the vapor recovery, but above the burp problem. If any gas station recovery system would fail, I would hope anyone driving would have an IQ big enough to know that the Prius won't hold 987 gallons, or even 12 gallons. :lol: I understand your concern for the environment since I have it too. I think this would prevent a lot of fuel belching on the ground as it does now from time to time with new owners.
     

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  7. FarmGeek

    FarmGeek New Member

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    I have never had a burp and I get consist readings and fill ups. Doesn't matter what station or pump.

    I fill the first 4-5 gallons at full speed and then hold the pump handle at the slowest speed for the rest of the fill up. I'm able to pump 5-7 more shut offs after the first shut off. Usually getting another .5 - .75 gallons in the bladder/tank.

    I have had the pump shutoff a couple of times on full speed and had to take the nozzle out enough to get the back pressure released.

    With close to 28000 miles in ten months, I'm real happy with the Prius.
     
  8. ScottY

    ScottY New Member

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    Cheap! I think your diagram is pretty neat and should solve this problem without causing extra environmental damage.

    Let me suggest an easier solution. Fill up, stop at first click, fill up again when "guess" guage down to 1 or 2 bars.
     
    Loscarrithers likes this.
  9. eagle33199

    eagle33199 Platinum Member

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    I'm not really sure i (or any of us, really) am qualified to tell how such a proposed system would handle in terms of gas pumps and vapor emissions.

    Regardless, i'll say it's an interesting idea. However, i think you would need several things to be able to pull it off: first, someone who's out of warrenty (you'd have to be crazy to invalidate much of the warrenty with something like this). Second, a mechanic willing to take the plunge. and third, a fluid flow expert (i have one in mind, actually), to model the situation properly and determine if it would actually work. oh, and maybe fourth, an expert on vapor emissions and gas pump design.

    needless to say, i think all it will ever really be is a diagram on a website.
     
  10. Leo

    Leo Leo

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    I had thought the solution would be a one-way trap on the filler pipe, that would permit fuel to go into the bladder, but prevent it from coming out.
    As I understand it, the filler pipe has a rubber gasket that fits snuggly around the pump nozzle, and this gasket prevents displaced air or gas from flowing back up past the nozzle. So as the bladder becomes full, adding additional fuel causes the bladder to stretch somewhat (especially if there is any air in the bladder, which would compress). When you pull out the nozzle, the pressure forces some of the fuel back out the filler pipe.
    Because the bladder collapses around the fuel, the engineers probably did not feel that a pipe to vent displaced air was necessary.
    However, the problem with my suggestion of a one-way trap is that it might cause the fuel in the bladder to be under some pressure, which would then force the fuel into the fuel injectors if it couldn't escape through the nozzle.
     
  11. Cheap!

    Cheap! New Member

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    <div class='quotetop'>QUOTE(eagle33199 @ Oct 24 2006, 03:02 PM) [snapback]337551[/snapback]</div>
    :lol: :lol: :lol:
    Well said! I'm good with ideas, not the follow through. Only other idea is to snake a small soft hose inside the bladder and "hope" you have the far end at the top of the bladder. Then cut the end short of the flap that prevents fuel from sloshing out. That way you would have a place for the trapped air to escape to, but the bladder would not have to be operated on.

    Do any of you want to try it? :rolleyes:
     
  12. mikel 52

    mikel 52 Member

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    I have a '67 Mustang with the gas cap in the back under the trunk lock not on the side of the car. And it does not like the modern day gas nozzles, it will make the pump shut off and/or burp and spit back unless you stand there and hold the nozzle in the right position and fill the tank very slowly.
    One morning in a stroke of genius I pulled a hunk of fuel line out of the trunk and snaked it in the filler neck along with the nozzle to vent the tank while it filled, and it solved the problem. I could run the pump almost full open without spilling any gas. Just have to make sure the gas fume police aren't watching while I fill it up.
    So the vent tube idea does work.

    Mike
     
  13. eagle33199

    eagle33199 Platinum Member

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    Yes, it may make pumping better, but all those fumes that are released are absolutely horrible for the environment, and it's also one of the reasons the Prius is such a good car - those fumes are virtually eliminated.
     
  14. daronspicher

    daronspicher Active Member

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    Who has had the gas tank apart that knows if this diagram is correct.

    There are two choices: When the gas tank is full, the bladder is empty (gas is in the tank, the bladder is empty and as gas is used the bladder expands to fill the vapor space).

    The other choice is as the diagram indicates. The gas goes inside the bladder and when the gas tank is full, the bladder is full. As the gas goes out, there must be some air-space between the 1/2 full bladder and the metal side of the tank.

    I thought it was the first way... Does anyone know for sure?

    What I would like to see is a mod where I replace the filler tube with a modified filler tube that is primarily just like the one we already have, except, it has a bulge in it and holds about 2 or 3 more gallons.

    I'm not concerned about vapors or the environment..
     
  15. eagle33199

    eagle33199 Platinum Member

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    <div class='quotetop'>QUOTE(daronspicher @ Oct 25 2006, 10:31 AM) [snapback]337996[/snapback]</div>
    I'll try to repress my desire to flame for the last comment....

    I've always been under the impression that it was the second way, gas flows into the bladder which then compresses around it, sort of like filling a water balloon.

    As for such a mod... i fail to see what it would ultimately do in the long run. it's essentially like asking someone to stick a second gas tank into the car - if you have two tanks and one feeds into the other which then feeds into the engine, then why not just have two tanks? I also don't think such a situation would solve the problem people are trying solve here, as you would still develop the same amount of pressure that would shut off the gas pump prematurely. Sure, you may think of it now as having a "safety factor" from gas spitting back out, but later you would probably just be thinking "well, i now have an 11.9 gallon tank plus a 2 gallon filler tube... the car can hold almost 14 gallons! why did it shutoff here at only 10.5?"

    I doubt you'll get much support here for any mod that increases emissions, not to mention voids the warranty on a pretty significant part of the car (modifying the filler tube could, potentially, void the warranty on the bladder, fuel tank, fuel pump, etc, should problems arise)
     
  16. galaxee

    galaxee mostly benevolent

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    dh has had a bladder tank out of a car at work... he said it's pretty much impossible to separate the two. the bladder IS the tank, which is then enclosed by a metal tank on the outside, likely to protect the bladder.

    there is a very complex emissions system to keep tabs on vapors... i have a feeling that tinkering with any of this would cause a permanent check engine light...
     
  17. echase

    echase New Member

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    OMG... where should I start this flame!?

    You guys are determined to defeat one of the key enviromental features of this vehicle, an hopes of getting what, an extra gallon in the tank!? Is this the same group that tries to maximize thier fuel economy? That extra gallon that you *might* be able to get with such a contraption is going to save you 50 miles between fillups, at the expense of 10 gallons of gasoline vapor discharged into the atmosphere, invalidation of your warranty, potential feul or vapor leaks, and an extra 10 pounds of weight on the vehichle!

    THIS IS A BAD IDEA. We are *not* smarter than Toyota's team of engineers.

    If you guys are serious aboout feul economy... consider this: fill your tank only half full this way you are not carrying an extra 50 ounds of uneeded weight. This will get you 200-250 miles between fillups, and no gas on your shoes.

    If somone here is hell-bent on making this work, you will need to install a check valve in the burp line, the bladder is designed to deflate as the feul emplties, which is also a safety feature, since you will not be driving with a tank full of explosive vapors when your gas is near empty.

    /END RANT
     
  18. fphinney

    fphinney Member

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    Bad idea!? Please re-think -

    I have always heard that one shouldn't fill gas tanks too full, by trying to add more fuel after the first 'click.' There is a charcoal canister (or EVAP system) somewhere around top of the gas tank. It absorbs and stores gas fumes from the fuel tank rather than allowing the fumes to vent to atmosphere. If your fuel tank is overfilled, the charcoal canister will be filled with raw fuel and be rendered useless, causing the engine light to illuminate. Other items attached to the EVAP canister, such as the vent shut valve and bypass solenoid, can also be damaged by overfilling. In fact, over-filling the fuel tank is the single biggest cause of evaporative emissions equipment failure. Fortunately, all you have to do to prevent these failures is to stop filling when the nozzle first shuts off.
    Generally, failures of this sort often occur on vehicles whose owners insist on rocking their vehicle side to side while topping up their gas tank, or by repeated 'clicking.'
     
  19. Syclone

    Syclone Member

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  20. daronspicher

    daronspicher Active Member

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    <div class='quotetop'>QUOTE(Greenkeeper @ Oct 25 2006, 11:10 AM) [snapback]338027[/snapback]</div>
    In the summer, I'm ok because I can drive to work and back 4 days and fill up shortly after I'm at 1 bar remaining, or maybe I'm still seeing 2.

    In the fall or winter, I'm white-knuckling it into the station on day 4, wishing this thing had another 2 or 3 gallon capaicity.

    All I get from such a contraption is less stops at the gas station.


    <div class='quotetop'>QUOTE(Greenkeeper @ Oct 25 2006, 11:10 AM) [snapback]338027[/snapback]</div>
    You probably aren't, don't speak for the rest of us.

    I'm not sure which Toyota genius decided on an 11.xx gallon gas tank. From what I've seen, they could have fit a 12 or 14 gallon tank which would have served me much better than this flaky POS system. They should look to the airline industry to find a fuel gague system that is a bit more accurate now that they know their driver base is tired of stopping for gas every 2 or 3 days.

    <div class='quotetop'>QUOTE(Greenkeeper @ Oct 25 2006, 11:10 AM) [snapback]338027[/snapback]</div>
    Nope.. Not hell bent on economy.. I'm at 52.2 avg over 8 months/ 30k miles and happy with it. I wouldn't say hell bent.. Not everyone is... Not everyone is all bunched up over a few escaping vapors either.

    I'm not sure what to say about this vapor canister and the warning light coming on. I typically add from .4 to 1.2 gallons after click off without spilling any gas or getting burped on. A time or two, I found myself filled to the neck and have not had any warning lights kick on.

    Give me a filler tube with a 2 gallon bulge in it and I'm sure I'll be just fine.
     
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